S65/S85 Throttle Actuator
The following information is provided for reference purposes only and should be used at your own risk.
In no event shall Beisan Systems, LLC or its members be liable for incidental, consequential, or special loss or damages of any kind however caused.
Introduction
An automotive throttle actuator is an electromechanical device that positions the opening of an engine throttle. Specifically, an engine throttle is a valve that controls the air intake into the engine. Typically, a throttle is a spring-loaded, default-position-closed butterfly valve. For example, the S65/S85 engine has 8 or 10 cylinders and is a V-type engine. Thus there are two engine head banks with each having 4/5 cylinders. Each cylinder has a dedicated throttle.
Thus each bank has 4/5 throttles. A single mechanical rail simultaneously controls these four or five throttles, ensuring they maintain identical positions. A single throttle actuator controls each throttle rail, which includes a row of four or five throttles. Therefore there are 2 throttle actuators, one for each engine bank.
The S65/S85 throttle actuator is an intelligent device that includes a microcontroller with a microprocessor, RAM, and ROM. Additionally, it connects to a CAN (Controller Area Network) bus. Through this connection, it communicates with the DME (Digital Motor Electronics, the engine computer) to receive commands for adjusting the throttle opening position.
It also connects to two throttle position sensors, one at each end of the throttle rail, which provide throttle opening position data for feedback control. The throttle actuator incorporates a DC (direct current) brush motor and two stepdown gears for throttle opening physical control. Two sets of transistor banks, each with two power transistors connected in series, drive the DC motor, enabling rotational and counter-rotational movement.
PWM (pulse width modulation) signal drives the motor. Essentially, a PWM signal is a square wave. The high pulse rotates the motor in one direction, while the low pulse moves it in the opposite direction. However, the frequency (cycle time) of this signal remains undocumented.
In addition, modulation (adjusting) of the PWM duty cycle (the length of the pulses) controls both the motor’s rotation and counter-rotation. Consequently, this determines the position of the throttle rail and the throttle’s open position.
The S65/S85 throttle actuator is prone to multiple failures, with an expected lifespan of approximately 70,000 miles.
One of the primary failures involves worn teeth on the step-down plastic gears. Notably, these gears are made of PPA (Polyphthalamide) plastic with fillers. Over time, the throttle spring load and engine vibration cause the plastic gear teeth to press against each other with significant force. As a result, continuous friction occurs, which leads to wear and eventual failure.
As a result, this intense contact and rubbing cause excessive gear wear, eventually leading to failure.
Moreover, one of the two main electronic failures of the throttle actuator occurs in the PC (printed circuit) board. Specifically, the voltage regulator IC (integrated circuit, chip), which is responsible for stabilizing the board’s input voltage, tends to fail over time.
This voltage regulator IC is a problematic part which degrades and eventually fails. It causes relative slow function of the throttle actuator as it degrades, and full throttle actuator failure once it fully fails. It can also cause the EEPROM and CAN bus driver power transistor to fail.
The second primary electronics failure is the PC board DC motor driving power transistors. High voltage spikes from the DC motor, occurring when the PWM signal reverses the motor’s driving polarity (i.e., during rotation/counter-rotation reversal), cause the transistors to fail. The throttle actuator has circuity to dampen the voltage spikes.
This includes a large capacitor located under the plastic cover bulge on the outer side of the throttle actuator cover. Although the circuity and capacitor are sufficient to protect the power transistors during “normal” function, the voltage spikes from the motor increase beyond the capabilities of the circuitry and capacitor and this exposes the transistors to voltage spikes that eventually cause them to fail. The cause of the higher voltage spikes is buildup of carbon dust from wearing motor brushes that interferes with the contact of the motor brushes to the motor commutator and increases the contact resistance.
A more rare failure is DC motor internal brush housing plastic melting. This occurs from high heat generated from brush carbon dust buildup and electricity. When this occurs, the DC motor can malfunction. If a PC board lead DC motor power transistor appears darkened (burnt out), then there is a chance that the DC motor brush housing plastic has melted.
Lastly, the DC motor brushes wear and are not replaceable. But indications are the brushes wear slowly and will last the lifespan of the car.
You can acquire new throttle actuator gears with a shaft from Beisan Systems (www.beisansystems.com). These gears are made from sintered and hardened powder metal steel, reaching 55 HRC (bearing steel hardness). They have a surface alloy finish from tempering that deters rusting. The half gear has a pressed-in stainless steel shaft, hardened to 50 HRC with a ground surface finish. The gears” hardened steel is over engineered for the throttle actuator application, and thus the gear teeth should never wear. This stainless steel shaft is made from the same stainless steel, and hardened to the same degree, as the OE (original equipment) shaft, so it should never wear.
A throttle actuator electronics rebuild service is provided by Bimmer Throttle Repair, www.bimmerthrottlerepair.com. The repair process includes replacing the four power transistors that drive the DC motor with new original equipment (OE) transistors. Furthermore, a redesigned voltage regulator replaces the original, addressing the common problems of degradation and failure. The rebuilt electronics undergo testing and assessment on an S65 engine test bed. If the EEPROM has failed, a new OE EEPROM replaces it. Likewise, a failed CAN bus transistor is replaced with a new OE version. These repairs, tests, and additional measures address nearly all (99.9%) electronic failures. However, if the electronics are still not functioning after these procedures, we will contact the customer and offer replacement rebuilt electronics for an additional $70.
This procedure shows how to clean the DC motor to remove the brush carbon dust and prevent the PC board power transistors from failing and brushes plastic housing from melting. It also shows how to test the motor continuity to check for internal melted brushes housing plastic. Inspect the DC motor brush length to estimate the remaining lifespan of the brushes and motor.
The Throttle Valve Actuator will need cleaning every 60k miles (100k km). This cleaning removes carbon dust buildup from the brushes and helps prevent potential damage. Specifically, it protects the PC board DC motor power transistors and the plastic housing of the DC motor brushes.
Symptoms
Limp mode, loss of power, DSC and EML lights
Diagnosis
One or more of the following fault codes:
P0638 (2B15): Throttle Actuator Control Range/Performance Bank 1
P0639 (2B16): Throttle Actuator Control Range/Performance Bank 2
2B21: Throttle Valve Actuator Pre-drive Check Bank 1
2B22: Throttle Valve Actuator Pre-drive Check Bank 2
2B25: Throttle Valve Monitoring Bank 1
2B26: Throttle Valve Monitoring Bank 2
Repair Procedure
The following is an E9X/E60 M3/M5 throttle actuators rebuild R&R (remove and replace) procedure.
Repair time: 3 hours mechanic, 4+ hours DIY.
Parts, Tools, and Shop Supplies
You can acquire BMW parts (part number pattern xx-xx-x-xxx-xxx) from a BMW dealership. Beisan Systems only provides the throttle actuator gears and throttle actuator press nut.
[BS101] S65/S85 Throttle Valve Actuator- includes 1 set of gears @ $250/set. You will need to purchase 2 sets to complete both actuators. S65/S85 throttle actuator press nut (BS191) $10/each. https://beisansystems.com/product/bs101-s65-s85-throttle-actuator-gears/
Note: The gears are made from highly hardened steel. Gold color is an alloy surface finish.
2 x S65/S85 throttle actuator electronics rebuild and test service $70/each (www.bimmerthrottlerepair.com)
Note: Only offered for US and Canada customers.
Electronics rebuild service is a must due to degrading and chronically failing voltage regulator IC. All throttle actuators will experience this degradation and failure.
Send the electronics (throttle actuator cover) to Bimmer Throttle Repair for a one-day rebuild and test service.
Bimmer Throttle Repair performs following work.
Replace the four DC motor driving power transistors with new OE (original equipment) transistors.
Install an updated OE voltage regulator, which resolves degradation and failure issues.
Swap the EEPROM for a brand-new OE version.
Finally, replace the CAN bus transistor with a new OE component.
Test electronics on S65 engine test bed.
If electronics is failed (< .1% of cases), customer is contacted and offered replacement rebuilt electronics for additional $70.
16mm socket 3/8″, 13mm socket 3/8″, T30 torx bit socket 1/4″, 3/8″ to 1/4″ socket adapter
3/8″ short-arm ratchet
3/8″ torque wrench (8 Nm [6 ft-lb]), 14 Nm [10 ft-lb]) (not shown)
Metric feeler gauges, including range .30-.40 mm (not shown)
2 lb handheld sledgehammer
Note: A torque wrench is unnecessary because the small torque values required are not critical and can be determined by feel.
Digital caliper, digital multimeter, alligator clip wires
Note: You will need tools to assess the DC motor.
To begin, gather the following materials: paper towels, a water-based cleaner (e.g., Simple Green diluted 10:1), and brake cleaner. Additionally, prepare a flat piece of wood (1″x4″x5.5″), synthetic grease that is non-separating and non-gumming (such as Super Lube), an oil lubricant with a dropper (e.g., 3-in-One), cotton swabs, and a parts plate.
Repair Process:
Future revisions will document the removal and installation of throttle actuators on the car. In the meantime, this guide focuses on the rebuilding of throttle actuators.
Perform the following work on a table to prevent parts from falling and becoming damaged.
Perform following throttle actuator rebuild for each throttle actuator.
Disassembly of throttle actuator
Spray clean throttle actuator external body (brake cleaner / towels).
Rotate throttle actuator shaft arm through full rotation range to get sense of operation.
Partially rotate and wiggle the shaft arm to get a sense of the gear tooth fit. Push and pull the shaft in and out of the throttle actuator to gauge the amount of play (space) between the shaft and the actuator.
Remove the Throttle Valve Actuator cover mounting bolts.
Using a T20 Torx bit socket (1/4″) with a 3/8″ to 1/4″ adapter and a 3/8″ ratchet, take out the five bolts.
Carefully lift and remove the throttle actuator cover. Next, pull the cover off from the electrical connector and set it aside.
Note: A tiny black plastic grommet may tear off during this process. However, this part is not needed and can be safely discarded.
Remove combo gear from throttle actuator.
Pull combo gear straight off mounting shaft.
First, visually inspect the throttle actuator shaft arm, mounting nut, and associated washers. Notice that the arm ball is oriented toward the side and rear of the throttle actuator.
Next, check the arrangement of the washers. Two small washers are located between the mounting nut and the arm. Additionally, a thick press washer is positioned between the arm and the throttle actuator housing. Finally, a small thin washer is placed between the thick press washer and the throttle actuator housing.
These parts will be removed in following steps.
Remove shaft mounting nut.Throttle Valve Actuator
Remove nut (13mm hex socket 3/8″ / 3/8″ ratchet).
Note: Rotate shaft arm to end of rotation range, then press down on arm ball on table and break nut seize. Place pad under arm ball (flat wood).
Remove shaft two small ribbed washers.
Pull washers off shaft.
Note: Washers tight ribbed side is oriented one to arm and one to mounting nut.
Remove shaft arm.
Pull arm off shaft.
Remove thick press washer from shaft.
Place throttle actuator on flat surface with shaft pointing up (flat wood / ground).
Moderately strike shaft end multiple times into throttle actuator until thick press washer is removed from shaft (2lb handheld sledgehammer).
Note: Perform work on very solid surface or ground.
Note: Shaft will be pushed into throttle actuator and thick press washer and small thin washer will fall off throttle actuator.
Collect fallen thick press washer and small thin washer.
Remove half gear with shaft.
Rotate half gear counter-clockwise to release spring hook from half gear slot, then pull half gear and shaft straight out of throttle actuator.
Remove large thin washer from half gear shaft.
Pull washer straight off shaft.
First, remove the two mounting bolts securing the DC motor. Use a T20 Torx bit socket (1/4″) with a 3/8″ to 1/4″ socket adapter and a 3/8″ ratchet for this step.
Note: Once the bolts are removed, observe that the DC motor bracket’s bolt holes are pressed onto the throttle actuator’s mounting studs.
Dislodge DC motor from throttle actuator housing.
Hit throttle actuator with open face down on flat surface (flat wood).
Repeat hit until DC motor dislodges from throttle actuator housing.
Note: DC motor bracket is press fit onto throttle actuator housing and requires some force to dislodge.
Remove DC motor and half gear spring.
Pull dislodged DC motor and spring straight out of throttle actuator.
The throttle actuator housing is now empty. Note: The throttle actuator housing is normally dirty with black dust from the DC motor carbon brushes. Next, proceed with the cleaning and inspection of the throttle actuator components. Finally, discard the throttle actuator gears, as they will be replaced.
Spray clean all throttle actuator components, except electronics/cover (brake cleaner / towels).
Be sure to clean both radial roller bearings, which mount half gear shaft, in throttle actuator housing.
Note: Also spray clean new gears and shaft as they can have residue.
Spray cleaner into DC motor from both end available openings until cleaner runs clear from motor (brake cleaner). Black residue from motor is brush carbon dust.
Motor top end (gear end) opening is adjacent to one brush on outer side (picture below).
Motor bottom end opening is small hole at bottom face.
Caution: DC motor must be cleaned per above instructions before performing following test.
To test the DC motor continuity, start by clamping the digital multimeter probes (equipped with alligator clip wires) onto the DC motor prongs. Next, turn on the digital multimeter and set it to measure low ohms (resistance).
Then, slowly turn the DC motor gear while observing the digital multimeter’s ohm reading. As you turn the gear, the reading will fluctuate. However, the reading should remain within the range of 0.5 to 3 ohms.
If DC motor resistance reading is high, then DC motor likely has internal damage from melted brush housing plastic and must be replaced. Contact Beisan Systems for possible options.
Inspect DC motor brushes length.
Measure, in mm, depth of 2 brushes in motor housing (digital caliper).
Open caliper jaws, then place caliper end extending rod on brush end and push down on caliper until caliper end mates with motor housing. Caliper reading is brush end depth from motor housing.
Subtract 4.5mm from measured depth value to remove motor housing thickness (2.5mm) and original (new) brush depth in plastic housing (2mm).
Remaining depth value is brush length wear.
Carbon brush length when new is 10mm.
Remaining brush is 10mm ” brush length wear.
First, inspect the throttle actuator electronics. Specifically, the four IC chips, each with two pins adjacent to the DC motor prong sockets (see picture top left), are the DC motor power transistors. Additionally, the IC with two double pins (see picture bottom center edge) is the problematic voltage regulator. Furthermore, the small 8-pin IC adjacent to the voltage regulator is the EEPROM (see picture just left and above of voltage regulator). Also, the 2-pin IC adjacent to the connector (see picture right bottom) is the CAN bus driver power transistor. Finally, the thick brown coating on the electronics is a conformal coating, which provides protection from corrosion, electrical shorting from debris, and solder cracking from vibration.
Assembly of throttle actuator
Lubricate the DC motor shaft radial bearings by placing one drop of oil at each end of the shaft. Then, rotate the DC motor gear to work the lubricant into the bearings. Finally, wipe off any excess oil with towels. Remember that the DC motor gear is mounted on the DC motor shaft; place oil under the gear and allow it to trickle into the radial bearing beneath it.
Apply grease to DC motor gear teeth.
Apply light layer of grease to gear teeth (bearing grease / cotton swab).
Note: Apply grease onto applicator, then swipe applicator along each tooth valley.
Insert DC motor into throttle actuator.
Orient DC motor with prongs at bottom and bolt mounting holes aligned to throttle actuator bolt mounting holes (picture).
Note: DC motor will be pressed into throttle actuator in following step.
To install the DC motor mounting bolts, first, install the two bolts using a T20 torx bit socket (1/4″ drive) with a 3/8″ to 1/4″ socket adapter and a 3/8″ ratchet. Once the bolts make contact with the DC motor, tighten them evenly in multiple passes. This ensures the DC motor bracket bolt holes are pressed evenly onto the throttle actuator housing mounting studs. Finally, fully tighten the bolts to 8 Nm (6 ft-lb) using the same T20 torx bit socket, adapter, and a 3/8″ torque wrench. However, it’s worth noting that hand-tightening with a ratchet is sufficient, and a torque wrench is not strictly necessary.
Apply grease to throttle actuator radial bearings and adjacent face surfaces.
Apply light layer of grease to 2 radial bearings (holes inner surface) and adjacent face surfaces (grease / cotton swab).
Note: Apply grease onto applicator, then roll applicator over radial bearing rollers.
Apply grease to half gear teeth.
Apply light layer of grease to gear teeth (grease / cotton swab).
Note: Apply grease onto applicator, then swipe applicator along each tooth valley.
Apply grease to half gear shaft and gear base.
Apply light layer of grease to shaft and half gear base face adjacent to shaft (grease / cotton swab).
Do not grease shaft threads and flats section and ~10mm (~1/2″) of shaft past threads base (picture).
Apply grease to the large, thin washer, and then install it onto the half-gear shaft. Use a cotton swab to apply a light layer of grease to both faces of the washer. Afterward, install the washer onto the half-gear shaft and slide it up against the half gear.
To install the spring in the throttle actuator, first orient the spring with the 90-degree bend facing the throttle actuator. Then, rotate the spring to align the bend with the slot in the actuator (as shown in the picture). Finally, insert the spring into the throttle actuator. Be aware that the spring will only insert slightly at this point.
Install spring further into throttle actuator.
Coil (wind) spring, from hook end, ~1 rotation while pressing spring into throttle actuator.
Spring will insert slightly further into throttle actuator, and spring hook end will be positioned further clockwise (picture).
Note: This step is performed to further insert spring and prevent it from falling out of throttle actuator.
Note: Exact amount of spring insertion and rotational position of spring hook end does not need to be precise. Spring will be fully installed in upcoming step.
Install half gear and shaft with large thin washer into throttle actuator.
Note position of spring hook end in throttle actuator housing.
Align half gear shaft end with throttle actuator radial bearing (hole) and insert shaft into radial bearing.
Insert half gear and shaft into throttle actuator housing until half gear butts with spring.
As needed, rotate half gear counter-clockwise until spring hook appears at side of half gear (picture).
Insert spring hook end into half gear slot.
Press in on spring hook end and slide behind half gear.
Rotate half gear clockwise ~1/2″, while pressing spring hook to center slightly, until spring hook insets into half gear slot (picture).
Coil (wind) spring, and fully insert half gear into throttle actuator.
Rotate half gear clockwise ~1 1/4 rotation against spring tension until half gear side is past housing gear stop ledge.
Then push half gear further into housing and release to allow half gear side to rest on housing gear stop ledge.
Important: Partially pull out the half-gear to allow full rotation without hitting the housing gear stop ledge. Important: The spring is now fully inserted into the housing and coiled to a smaller size.
Caution: In the next steps, ensure the half-gear remains in position, as it can easily slip out.
Apply grease to small thin washer and install onto shaft.
Apply light layer of grease to washer faces (grease / cotton swab).
Install washer onto shaft and slide washer up to throttle actuator housing.
Note: Press on half gear in throttle actuator to prevent it from dislodging (fingers).
Mount thick press washer onto shaft.
Apply thin layer of grease to one face of thick washer.
Mount thick washer, greased face first, onto shaft wide diameter edge.
Note: Press on half gear in throttle actuator to prevent it from dislodging (fingers).
Install press nut.
Thread press nut, inner recess side first, onto shaft, and up to thick press washer (fingers).
Note: Press nut will be difficult to initially thread onto shaft due to minimal shaft threads. Position press nut perfectly perpendicular to shaft to ease initial threading.
Note: Press on half gear in throttle actuator to prevent it from dislodging.
Press thick press washer onto shaft.
Tighten press nut to press washer onto shaft (16mm hex socket 3/8″ / 3/8″ ratchet).
Tighten press nut until stop. Do not further tighten.
Note: Washer press takes minimal force.
Remove press nut form shaft (16mm hex socket 3/8″ / 3/8″ ratchet).
Attempt to rotate half gear (finger) and note binding and lack of free rotation.
Slightly retard (un-press) thick press washer on shaft to resolve binding and allow gear/shaft rotation.
Place throttle actuator on flat surface with shaft pointing up (flat wood).
Lightly tap shaft end into throttle actuator (2lb handheld sledgehammer).
Note: Only slight retard of thick press washer on shaft is needed to release binding.
Verify half gear rotates freely through full range of rotation without binding (finger).
If half gear is binding, repeat above step of slightly retarding thick washer, and check binding again.
Check and adjust space between thick press washer and small thin washer.
Pull shaft from throttle actuator.
Measure space between thick press washer and small thin washer (feeler gauges).
Adjust thick press washer position, by pressing or un-pressing per above steps, to achieve ~.35mm space.
Available feeler gauge smaller than .35mm should fit in space, and available feeler gauge larger than .35mm should not fit in space (pictures).
Note: ~.35mm space is needed to prevent binding and allow gear/shaft rotation, but also prevent excessive gear/shaft axial (in/out) movement.
Install shaft arm onto shaft.
Orient shaft arm with ball to side and rear of throttle actuator (picture), and slide arm slot onto shaft end flats.
Install 2 small ribbed washers onto shaft.
Place first washer with tight ribbed side towards shaft arm (picture).
Place second washer with tight ribbed side away from shaft arm (picture).
Note: Washers are Nord-Lock washers and prevent nut, mounted in following step, from coming loose.
Caution: If the washers are not oriented correctly, the nut installed in the next step may loosen due to engine vibration.
Install shaft mounting nut.
Thread nut onto shaft with face inscription side away from arm.
Note: Nut will be difficult to initially thread onto shaft due to minimal shaft threads. Position nut perfectly perpendicular to shaft to ease initial threading.
Tighten shaft mounting nut.
Tighten nut (13mm hex socket 3/8″ / 3/8″ ratchet).
Fully tighten, 14 Nm (10 ft-lb) (13mm hex socket 3/8″ / 3/8″ torque wrench).
Note: Moderately tighten w/ ratchet. Torque wrench not necessary.
Apply grease to the throttle actuator combo gear mounting shaft and base surface. Apply a light layer of grease using a cotton swab.
Also, apply grease to the combo gear teeth, using a light layer on both the small and large diameter teeth, as well as the small gear end surface. For better precision, you can use a cotton swab again for this step.
Note: Apply grease onto applicator, then swipe applicator along each tooth valley.
Install combo gear.
Insert combo gear, small gear side first, onto throttle actuator mounting shaft.
Slightly rotate combo gear to fully insert and mate teeth with DC motor gear teeth and half gear teeth (picture).
Exercise throttle actuator mechanical operation.
Note: Do not tilt throttle actuator opening down as combo gear can fall out.
Rotate throttle actuator arm through full rotation range and monitor movement of gears in throttle actuator.
Repeat shaft arm rotation multiple times to disperse gear teeth grease and achieve smooth operation.
Wipe off visible excess grease from gear teeth ends (towels).
Partially rotate and wiggle the shaft arm to assess the gear teeth fit.
Slowly rotate throttle actuator arm through full rotation range and note any gears binding. If you notice any binding, contact Beisan Systems.
Install the throttle actuator electronics and cover after receiving the rebuilt electronics.
Repeat throttle actuator rebuild for second throttle actuator.
Send electronics for rebuild and test service
Purchase 2 x S65/S85 throttle actuator electronics rebuild and test service $70/each (www.bimmerthrottlerepair.com).
Note: Only offered for US and Canada customers.
Package and ship 2 x throttle actuator electronics/cover to Bimmer Throttle Repair.
Wrap parts well to prevent damage, and ship with tracking service.
Ex, USPS Priority medium flat rate box.
Bimmer Throttle Repair
3305 Forest Mill Circle
Raleigh, NC 27616
Installation of electronics/cover
Warning: Clean the DC motor according to the instructions above.. Otherwise new electronics will shortly fail.
Once you receive the rebuilt and tested electronics, proceed with throttle electronics and cover installation.
Install throttle actuator electronics/cover.
Orient cover to throttle actuator housing.
Orient throttle actuator with DC motor prongs and electronics prong sockets at bottom, and throttle housing to front and cover to rear (picture).
Insert electronics prong sockets onto DC motor prongs.
Fully mate cover onto throttle actuator housing.
Note: Bend DC motor prongs as needed to align with electronics prong sockets.
Install throttle actuator cover mounting bolts.
Mount 5 bolts onto cover (T20 torx bit socket 1/4″ w/ 3/8″ to 1/4″ socket adapter / 3/8″ ratchet).
Tighten bolts in multiple passes to evenly tighten.
Fully tighten, 8 Nm (6 ft-lb) (T20 torx bit socket 1/4″ w/ 3/8″ to 1/4″ socket adapter / 3/8″ torque wrench).
Note: Hand snug w/ ratchet. Torque wrench not necessary.
Check mechanical operation of throttle actuator by rotating shaft arm through its full range of rotation.
Repeat electronics/cover installation for second throttle actuator.
Post repair procedures
Clean the DC motor every 60k miles (100k km) to remove brush carbon dust and prevent electronics failure.
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