R170 BAS/ESP/ABS/Wheel sensor & brake pedal - Mercedes Benz SLK Forum

Tires, Wheels, Brakes & Suspension Discussion and information regarding tires, wheels, brakes and suspension.

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#1 Old 01-12-2019
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R170 BAS/ESP/ABS/Wheel sensor & brake pedal

Sorry this is very long post!

I have been chasing a problem which may have started a few months ago when my check engine light came on. This may have been a coincidence! I read the codes on my Autel MD805 code reader which indicated P2026-4 (Y58/1(Purge control valve open circuit/switchover valve permanently closed. Due to travel over the holidays I put resolving this off. After not using the car for a week, I noticed the brake pedal seemed very spongy, but aside from checking/topping up fluid I didn't look into this further. Then a few weeks later the Brake, BAS/ESP/ABS and Wheel Sensor fault lights came on. I read the codes which indicated 3 ME/SFI faults as well as: P2026-4 (Y58/1(Purge control valve open circuit/switchover valve permanently closed (P0444)), P20CC-8 (Rough road detection by comparing wheel speeds) C1022-2, C1022-4 (Faulty can-bus communication) Event P2036-4 No or incorrect CAN message from unit N47-5 (ESP control unit) See also P0600), B1416 A31 m1 Coolant circulation pump, and a ICM instrument cluster with maintenance interval display fault. WOW!!!

After reading codes I erased them a few times and at one point got all dash fault lights to go off with MD805 indicating: "System Pass, No fault codes detected"... however shortly thereafter I had all the dash fault lights and codes come back on!

I read all past posts and took a stab at the ABS module, removing and inspecting the electronics in hope I had bad solder joints on the board/connector interface. Under careful (magnified inspection) I found solder joints to be good. I'm not sure where to start with the fault lights and codes so I have decided to look into the cause for brake pedal issue. With engine on and steady pressure on pedal it slowly goes down though not completely to the floor. My suspicion is that I might have a bad master cylinder as there is no visible fluid leakage. I'll first inspect and then bleed the system. If that doesn't alleviate the spongy/sinking brake pedal U plan to plug the front and rear M/C lines and replace the M/C if the pedal still sinks.

I would love to hear any ideas, observations or recommendations!

Gary
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#2 Old 01-12-2019
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I would reflow solder regardless. Not sure if you can always see micro fractures even under magnification.

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#3 Old 01-12-2019
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Have you tried replacing the brake pedal switch? This is very easy and cheap to do (just unclip the wiring harness and twist the brake pedal switch out to replace.
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#4 Old 01-13-2019
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Thanks, I will do that since this module has the larger number of codes associated with it however I am fairly certain that the solder joints are good. I spent my career as an electronics technician then later as quality assurance/reliability engineer and know what to look for during inspection. That being said I can only inspected one side of the SMT circuit board! In 2009 I had problems with the K40 relay board which had a large number of cold/fractured solder joints. I cleaned & reflowed the solder joints and have had no problem with this module since. My experience with the soldering on this assembly made it easy for me to suspect the other electronics modules in these cars.
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#5 Old 01-13-2019
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Thanks for the suggestion. I haven't looked at the brake switch yet due to the other fault codes and dash lights I am experiencing. I will certainly consider replacing it. I am wondering if anyone has experienced a bad brake light switch causing the dash Brake light to illuminate along with the ABS/ASP/BAS/and Brake Wear lights.

Logically it doesn't make sense to me that my car would all of a sudden developed failures in numerous system components. It seems most likely that I have one or perhaps two defects/failures accounting for the fault codes and lights displaying on my dash.

An earlier code I read was P0600 (serial communication link malfunction) which I believe is real and most likely points to a component that could if bad interrupt the serial communication (such as the N47 ABS electronics module). I would think a component not connected to the serial chain like the brake switch) is unlikely to cause the plethora of codes I am seeing.
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#6 Old 01-14-2019
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The brake switch is actually a brake pedal position sensor and does much more than just brake lights. A faulty one will cause the BAS ABS etc to illuminate as the electronic systems no longer have feedback from the brake pedal and, like any sensor or switch, it can just work one minute then fail the next.
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#7 Old 01-15-2019
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I pulled the N47-5 (ESP control unit) electronics module to re-solder the connector pins on the board. I used a manual solder sucker to remove the existing solder and inspected the pins. I was a bit surprised at how oxidized some of them were beneath the original solder. I hand soldered them all using old school 60/40 electronics grade solder and then removed the solder again until the flux in the solder cleaned off the surface corrosion. I had to do some 3 or 4 times to get the solder to properly wet the pins. I re-installed the electronics onto the brake solenoid block and cleared the codes. I got a "System Pass" with "No fault codes detected" off my OBD tool after clearing the codes and was somewhat hopeful because the codes didn't almost immediately come back even after running the engine a few times. I drove about a half a mile and the 4 brake fault lights came on momentarily then went off again.I forgot to mention that when the brake fault lights are on the speedo dies. Right after that the speedo died and the lights came back on this time with the "check engine" light.

When I returned I read the codes which were the same as prior to this. I cleared the codes and then read them again.

This time the codes read as follows:
1) "P20CC-3 (Rough road detection signal (by comparing wheel speeds) Speed signal from control module ESP implausable / Read out fault memory of control unit ESP (P1 999)"
2) "Event P2036-4" code: No or incorrect CAN message from control unit N47-5.(P0600)
3) "P2026-4" Y58/1 purge control valve permanently closed (P0600)
4) B1041 Fault in CAN communication with control unit Traction Systems
5 ) (Didn't read Code ???) Fault in ICM Instrument Cluster with Maintenance interval display

Does it make sense that the speedometer dies when the fault lights come on? Maybee the speedo dying (intermittently shorting?)is the cause of a fault and not the result of one?
Aside from a soft brake pedal and non-functional speedometer.. the car starts and runs fine!
Tomorrow I'll take a look at the brakes and wheel sensors & look further into the ICM fault

Gary
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#8 Old 01-15-2019
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I would say you have a faulty wheel sensor but I don't understand your fault codes.
It is possible to measure the resistance of each one if you remove the wheel and pull the connector. Put an ohms meter across the sensor and rotate the wheel hub and you should see a change in the ohms value as the reluctor ring passes the sensor. No reading will indicate a faulty sensor.
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#9 Old 01-15-2019
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I would say you have a faulty wheel sensor but I don't understand your fault codes.
It is possible to measure the resistance of each one if you remove the wheel and pull the connector. Put an ohms meter across the sensor and rotate the wheel hub and you should see a change in the ohms value as the reluctor ring passes the sensor. No reading will indicate a faulty sensor.
Thank you. My plan is to inspect/check all brake pads, calipers and sensors. I appreciate you elaborating on a method to confirm operation of the wheel sensors.

That being said I want to mention that I did get some other codes prior to this involving each individual wheel sensor as well as the air conditioning (TAC) system making me believe that the CAN bus related faults are to some extent erroneous and are at least to some extent pointing me in the wrong direction. I need to look further into how the CAN bus works.
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#10 Old 01-16-2019
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Today I checked the rear ABS sensors using a Fluke DVM (multimeter). I measured each sensor after disconnecting the cable from the chassis. Measuring between the pins, I measured 6.5 meg Meg-ohms (6.5 million ohms) on one side and 6.7 meg ohms on the other side. Both look like they are essentially "open" as the correct resistance should be in the range of 2,000 ohms! I changed the meter settings to ACV and checked for a small AC voltage, by rotating the brake rotor. No voltage on either wheel.

So It appears as if both rear wheel ABS sensors are bad! It doesn't seem at all likely that both sensors would fail at the same time! Could the ESP electronics have failed and taken out both sensors. Tomorrow I will check the front! I had previously seen failure codes indicating faults on multiple wheels however due to the large number of codes I was getting assumed that they were not real codes. I will have to re-test the ABS brake electronics tomorrow using my Autel MD805 scan tool.
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#11 Old 01-16-2019
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Today I checked the rear ABS sensors using a Fluke DVM (multimeter). I measured each sensor after disconnecting the cable from the chassis. Measuring between the pins, I measured 6.5 meg Meg-ohms (6.5 million ohms) on one side and 6.7 meg ohms on the other side. Both look like they are essentially "open" as the correct resistance should be in the range of 2,000 ohms! I changed the meter settings to ACV and checked for a small AC voltage, by rotating the brake rotor. No voltage on either wheel.

So It appears as if both rear wheel ABS sensors are bad! It doesn't seem at all likely that both sensors would fail at the same time! Could the ESP electronics have failed and taken out both sensors. Tomorrow I will check the front! I had previously seen failure codes indicating faults on multiple wheels however due to the large number of codes I was getting assumed that they were not real codes. I will have to re-test the ABS brake electronics tomorrow using my Autel MD805 scan tool.
You can rotate the brake rotor without rotating the axle. (if lug bolts are not screwed in) can you confirm the axle was spinning?
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#12 Old 01-16-2019
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The lug bolts were indeed off and the axle was turning. It appears that both wheel sensors are open. The reading I got was 6.5 meg ohms indicates an open! I believe the resistance should be in the range of 1-2 K ohms correct? Looks to me like both sensors are dead!

I tried to read the ESP module codes this morning but my scan tool cannot link with it. I know I previously was able to scan it because I saw fault codes for wheel sensors but now the scan tool just skips over the ESP module. On the scan I just tried I do however communicate with the ME/SFI computer so I know my tool should be able to link with ESP. Any idea where the fuse is for it? I checked the main fuse block and K40 relay fuses, not there, No blown fuses in in either fuse location!
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#13 Old 01-16-2019
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Your assumption that both rear sensors are faulty is correct as 6.5 megs is way to high. You are also correct that the true reading would be around 1.2 kohms for a working sensor.
The power for several modules and systems comes through the K40 including traction control so probably esp also but i'm not 100% sure. Perhaps @savcom might be able to help.
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#14 Old 01-16-2019
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From what I have the wheel speed sensors on the back of the car are inductive. They are therefore coils of wire that pick up a magnetic signal from a rotating toothed rotor. If you are measuring 6.5MΩ on the sensors then there is definitely something wrong. The suggested way to measure/diagnose issues is to measure at the plug to N47 as you can see below.

I've this info relating to how the three sensors work (you probably know this, but it all helps clear the picture):
The rear sensors are Inductive sensors. These are coils with magnetic cores installed at a defined distance from the rotor on the rear halfshafts or the drive pinion at the rear axle (i.e, on the diff). They work by having their magnetic field intersected by the teeth of a rotor. This changes the magnetic field and the coil induces an AC voltage. The frequency of this alternating current is governed by the number of teeth on the rotor and the speed of rotation so this frequency is proportional to wheelspeed.

The test info I have is as follows:
  • Disconnect N47-5 plug and measure 0.6-1.8 kOhms across pins 6 & 7 for left rear wheel and pins 35 & 36 for right rear wheel. See diagrams attached. (The two dotted lines at the top of the wiring extract represent the N47-5, the ESP and BAS control module).
  • To test, spin wheel at 1 rev/sec, measure at least 120 mVAC between both wires of sensor. If voltage is OK, measure the sensor's resistance while pulling, twisting and bending the sensor wires, looking for intermittent opens. Finally, check the sensor tip and rotor teeth for dirt or breakage. An oscilloscope can also be used to check the waveform. It should be a sine wave. Chipped or dirty teeth show up as missing or malformed waves.
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File Type: jpg N47-5 connector.jpg (29.9 KB, 2 views)
File Type: jpg N47-5 rear wheel sensors.jpg (17.3 KB, 3 views)

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#15 Old 01-16-2019
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The K40 link is shown in the diagram below. The two dotted lines at the top represent the N47-5, the ESP and BAS control module.
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#16 Old 01-17-2019
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Thank you Savcom for your detailed response. I found it very helpful!

So since I didn't have a probe small enough to probe the Speed Sensor (SS) pins on N47-5 connector I measured across the appropriate pins on the N47-5 board assembly. With power off I measured roughly 42K ohm on the left rear (pin 6/7) and right rear (35/36). I went ahead and measured the left front (3/4) and right front (32/33) Both measured roughly 48K ohm. I removed the connector and remeasured and got slightly higher readings 43K ohm = rear, 52K ohm. These readings are due to the internal source resistance of the board assembly. The readings should all have been 1K ohm with the connector attached. This shows that all of the speed sensors are "open" and need to be replaced. I am of the belief that when powered in operation 12V is applied to the speed sensors so it makes me think that they all failed due to age unless my 12V supply was hit by Lightning. I removed one of the front SS connectors and measured 0.7M ohm across indicating it is essentially "open". So now I have 4 bad speed sensors, not 2!

I checked and verified 12V (constant) supply to N47-5 Pins 45/47 +12V, and pins 44/46 V-.
I checked Pin 18 for 12V (traction control) which measured 0VDC.
The ESP switch on the dash appears "dead" and does not light up or provide power to N47-5, pin 18.
It appears that K40 Relay K5 is not engaging. K40, F1 is good and has 12V.
There is no DC voltage on the Speed Sensor contacts with the car running and N47-5 connector attached.
N47-5 has constant power being supplied but appears to be in a "stand by' awaiting one or more inputs.

I guess I need to find out why the traction control relay (K40 K5) isn't engaging!
Yesterday I found a schematics of the Braking system including N47-5
I also previously had schematics from troubleshooting the engine control electronics which includes K40 and ME/SFI assemblies.

So... if anyone has a suggestion on what might be preventing N47-5 from turning-on I am all ears!
Also I'd like to figure out why all 4 of my speed sensors are "pushing up dasies"

Gary
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Thank you Savcom for your detailed response. I found it very helpful!
You're welcome.

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I am of the belief that when powered in operation 12V is applied to the speed sensors so it makes me think that they all failed due to age unless my 12V supply was hit by Lightning. I removed one of the front SS connectors and measured 0.7M ohm across indicating it is essentially "open". So now I have 4 bad speed sensors, not 2!
Be careful here. From what I know I would not expect 12V to go anywhere near these (can someone please confirm??). I think the wheel sensors generate their voltage by consisting of a coil wrapped round a magnet, so that when the rotors turn a small electric current is generated (like a dynamo) by the interference of the magnetic field by the teeth on the rotor. which is detected by the N47.

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I checked and verified 12V (constant) supply to N47-5 Pins 45/47 +12V, and pins 44/46 V-.
I checked Pin 18 for 12V (traction control) which measured 0VDC.
The ESP switch on the dash appears "dead" and does not light up or provide power to N47-5, pin 18.
It appears that K40 Relay K5 is not engaging. K40, F1 is good and has 12V.
There is no DC voltage on the Speed Sensor contacts with the car running and N47-5 connector attached.
N47-5 has constant power being supplied but appears to be in a "stand by' awaiting one or more inputs.

I guess I need to find out why the traction control relay (K40 K5) isn't engaging!
Yesterday I found a schematics of the Braking system including N47-5
I also previously had schematics from troubleshooting the engine control electronics which includes K40 and ME/SFI assemblies.

So... if anyone has a suggestion on what might be preventing N47-5 from turning-on I am all ears!
Also I'd like to figure out why all 4 of my speed sensors are "pushing up dasies"
I'll see what more diagnostics I can find around the K40 and around the rest of N47, but you're right, it's difficult to imagine a scenario where all sensors have gone open circuit.

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Starting with the K40-k5, I've attached the wiring diagram. The diagnostic is that pin C4 (the one connecting N47-5) should go to +12V when the ignition is on. Note the relay output also feeds pin C5 which connects to the automatic transmission. I'd measure the K40 pins and see if they're at +12V. I'd also measure the voltage on C3. If that's not measuring +12V then look at the fuse near k5. if that's OK then continue backtracking as this circuit goes back the F1 fuse box too. On the diagram, the unit labelled 54.15-U-2000K is the Fuse and relay box (F1)

Can you hear/see relay k5 actuate at all? Are the contacts clean? Is k9 operating (as k9 is powered by the same source of 12V) If k9 is running, perhaps look for badly soldered joints around k5's coil.

Heh @glmce I've just noticed where you're based. If only we'd gotten in touch sooner. I was in St Pete's before Christmas, visiting the Dali Museum. Lovely place.
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I forgot to also to thank Stu32 for his help!

There are so many inputs/outputs connected to this assembly. It is not clear to me what the interaction is based on the schematic and the the component descriptions! It would be nice to have a write-up describing this assembly. I got a chuckle when I saw on the schematic that the ABS BAS, ESP and brake wear indicators are all wired together (in parallel). Hey..thats cheating! I guess Mercedes wants to get the owners attention when there is some sort of brake related fault! It worked on me!

The diagnostics is not nearly as sophisticated as I originally thought.

Back to the schematics

Thanks again!

Gary
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K40 C4 does not have 12V on it with the ignition "On" so that part of my brake problems must be in the K40. I will check relay K5 tomorrow morning. In any case that explains why I couldn't communicate and read the speed sensor codes on the ABS module. I'll feel better when I get it powered and see the Speed Sensor codes. Still is a mystery how all 4 speed sensors died. Something must have stressed them. I'm just hoping the ABS assembly is OK aside from the wheel sensors!

I'm not very adept (yet) at reading and using the MB schematics. I was able to download a few schematics online for free but my access to them is limited.What does the finger pointing to: PE ##.##-U-####XY mean? I assume it indicates the drawing # for the block it is in. Could you explain this a bit or direct me to where I can get some help with this? The last schematic you sent the thumbnail of was different from what I'm using. Can you tell me which one it is? Any pointers you could give would be greatly appreciated.

I would have enjoyed meeting you had we been in touch prior to your visit. The Dali Museum and St Pete in general is very nice. The weather here is much warmer than Boston (and other places up North) which is why I'm down here now!

Gary
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