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C.P.S. Issue

2K views 22 replies 6 participants last post by  silver7 
#1 ·
I have 2002 c320 wagon that is starting to show its age. 4 weeks ago, after a 40 minute drive and an hour cooldown, the engine would turn over but wouldn't start and had a check engine light. After an hour of researching online, I believed my problem to be the crankshaft position sensor. Another attempt to start the engine successfully got me to the parts store. Code reader confirmed C.P.S. fault.
Fast forward 4 weeks. Problem is back along with check engine light. Is this possibly a harness issue and not the sensor? Keep in mind that I paid $3900 for this car. "Workshop" diagnostics/repairs aren't in this cars future.
 
#3 ·
I can not remember the code. I won't buy MB parts unless all other options have been exhausted. The sensor is a duralast. I didn't have 4 days to wait for a Bosch. With that said, as an aircraft mechanic, I have never seen component failure repeat without a problem upstream.
 
#5 ·
I won't buy MB parts unless all other options have been exhausted. The sensor is a duralast. I didn't have 4 days to wait for a Bosch.
A Duralast crankshaft sensor at my AutoZone is $55.99 + tax. I can get a Bosch sent by next day air for $45.69 or OEM for $49.99 from RM European.

Keep an open mind Grasshopper............you still have a lot to learn :)
 
#4 ·
I can't tell you why cheap CPS's faile like that, but they really seem to do it. Even "Bosch" parts bought from unreliable sources (Amazon, eBay) tend to fail. it seems that the best thing to do is get a genuine MBZ or a Bosch from a reliable European auto parts specialist (autohausaz, pelicam, rmeuropean, eeuroparts, etc.)
 
#8 ·
If you are talking about P0335 (CKP code), with a multimeter in voltage setting to AC, you should be able to measure more than 2 VAC when cranking and more than 5VAC after start, on ECU pins 37e and 38e (where the CKP wiring terminates). You may have a bad connector / intermittent / resistive connection which can reduce the voltage below the acceptable range.
 
#11 ·
Update

So the C320 takes after its owner. Apparently it's a slow learner. I have had no issues with hard starting or stalling over the past 4 weeks but I did have an alternator die at 165k miles. CPS issue self repaired. Changed the battery with the alternator because it was installed in 2011. I had the undervoltage message once last summer but had dismissed it due to stop and go traffic in South Carolina mid afternoon in August. If I could just find a video to show me exactly what needs to be removed to fix those pesky flap actuators and related linkages. All hail the "Euro-Mom-Mobile" as my coworkers lovingly refer to it. She is a happy one again.:grin
 
#12 ·
After a change of a CPS, people do not realize that they need to do the sensor adaptation to de-sensitize against the CPS signaling, when going in rough roads / bumps. For your car, it involves in driving the car in 3rd gear, at 2,100 rpm for more than 30 seconds with engine coolant temp more than 70 degrees C. This will adapt the VSS to the changed CPS within the ECU.

If you do not do this, your car will be a slow learner, indeed :)
 
#14 ·
Check this out. (From Startek ME-SFI M112 engine)

Notes regarding VSS sensor adaption for rough running engine test:

After the replacement of the ME-SFI control module, CKP sensor (L5), starter ring gear, or motor mount, a sensor adaption must be performed:

•Engine coolant temperature approx. > 70 oC,
•Drive vehicle on road.

Vehicles up to 01/98:
•With selector lever in position 4: Increase engine rpm to approx.2,500 rpm and then coast until engine rpm is approx. < 1,500 rpm.
•With selector lever in position 2: Increase engine rpm to approx.6,100 rpm and then coast until engine rpm is approx. < 4,100 rpm.Again increase engine rpm to approx. 6,100 rpm and then coast until engine rpm is approx. < 3,000 rpm.
•Using the HHT, determine if VSS sensor adaption has taken place.

Vehicles as of 02/98:
•With selector lever in position 3: Increase engine rpm to approx.2,100 rpm and then hold a 50% engine load for approx. 30 seconds.
•Using the HHT, determine if VSS sensor adaption has taken place.
 
#16 ·
The ECU detects misfires from the shifted pulse timings received from the CPS. Excessive vibrations / jolts / rough running will cause changes in the pulse timings, and if no filtering done based on ECU algorithms, you would get lots of false misfire codes.

So the ECU "adapts" to suppress the false misfires over time as the mounts get worse, and jolts start getting more intense. When you change the mounts, the jolts become much smoother in intensity, but the ECU does not know that you changed the mounts. It then becomes possible to actually suppress real misfires unintentionally. By doing the adaptation, the ECU is more sensitized to pulse shifts.
 
#17 ·
interesting... I wonder if this is why parts store CPSs have such a significant "failure" rate.

This I can tell you with certainty, these cars were designed with a mechanic in mind. I have yet to find something on it that I could not do. I have large hands, getting to the cps was a challenge but not a struggle. I removed the battery and alternator, drove to get the alt. tested, drove back and installed new alt and battery in under 1.5h.

FYI I found a type 49 900cca Exide battery with a three year warranty for $119 at, of all places, Home Depot!

One day my thriftiness will be the death of me!!
 
#18 ·
My understanding is that misfires are detected by the knock sensor. Which cylinder is firing is determined by the angle of the crank, which is based on reports from the CPS. The adaptation is to help smooth out minor variances in the gaps on the flywheel that are detected by the CPS. I don't see anything in WIS that indicated this is to be done for motor mounts, but definitely for a new CPS or flywheel (a.k.a. flex plate). If it's not done, it might not cause any problems, but the engine could run at less than peak efficiency. It's possibly that if any of the flywheel gaps are far out of standard size/position, you could have misfires, but I think if they are that bad, you need a new flywheel.
 
#20 ·
To keep this discussion going I have a question. The other day the C240 stalled in hot weather near 110 degrees and threw P0720 fault code, but no CPS fault code was present. Could a bad CPS cause the stall which in turn caused the P0720 "Output Speed Sensor Circuit Malfunction"?..

Any ideas are appreciated.
 
#22 ·
After the stall did you mange to start the engine immediately ? If so, it is less likely a CPS issue. Usually you need to wait for the engine to cool off first for it to re-start with a flaky CPS..

The P0720 code is a code generated by the TCU complaining about communications issues with the Traction Control (N47) module regarding the implausible Vehicle speed sensor info. To find out if this is the TCU error or the N47 error, both modules need to be scanned with an MB Star or equivalent for codes.

A 110 degrees F temperature.. Probably the a/c is running at full capacity, with the cooling fan at maximum. you stop. The engine stalls. Are you sure your battery is good? When you have a lot of power consumers, and the alternator cannot supply demand (low rpm during stopped traffic), you start discharge from the battery. If the battery is weak the voltage drops, and the electronic modules start dropping too.
 
#23 ·
my son was driving and he said the engine did not shut down, just sputtered and he lost the power brakes momentarily, which was a bit scary on a busy road.

Is it possible i messed with the N47 module while replacing the brake pads two days earlier?

The battery was replaced last year with a battery from walmart. May be that was a mistake, This morning i checked the voltage and it was 12.4 V (engine off). May be this battery did not like the heat.

I will be getting the icarsoft scanner tomorrow hopefully i can scan some systems.

Thanks for the replies guys.
 
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