elphzwolf

Hello everyone.

I recently purchased a second hand 2001 w203 c200 with 120000km on it. Drove it for ~400km when the fuel and temp gauges went out: fuel gauge sits just below empty, and coolant temp gauge does not show the temperature (bar chart close to 0). Took it to the official MB service, they changed a broken thermostat and apart from that had not been able to identify a problem for the past 4 days. Considering your experience, does anybody have any idea what could be wrong with the gauges.


Thanks for any input/help in advance.

Russell Ormerod

It sounds like Two seperate issues, fuel gauge fault could be the sender in the tank itself. temp gauge could be the coolant sensor fault. Ask the dealer for the short test print out and post it here.

Glyn M Ruck

Could be a CAN B networking problem with the cluster. Please try & post codes.

elphzwolf

Thanks for your imput Glyn... Went to the dealers today. They said that the voltage of the CAN B was off (11V instead od 5V). So they stripped down all the control modules wired to the CAN B one by one, but the voltage didn't come down. They located the problem in the ignition lock control module (the one that's supposed to coordinate all of the modules wired via the CAN B). They suggested chaning the ignition lock and key (~$1200 US). Btw could not get the mechanic to give me an ODBII printout, however he mentioned something about the ODBII scanner being able to access all the modules wired via CAN A, the N73 (the ignition switch i think), but none of the modules wired via the CAN B network behind the N73. I consulted another local electronics guy that said he could fix my existing and the CAN B problem for under $200 in parts and labor. Hope it works out. Please feel free to add any and every kind of input. Will post as soon as I have any results (trying the cheaper option first).

Cheers.

Glyn M Ruck

I thought it was a CAN B problem, gauge failures are not common especially 2 at the same time. If your local electronics guy knows what he is doing I'm sure he can fix it. Dealers are parts replacers. They won't fix a module or whatever. The EIS is expensive & can also be repaired by a knowledgeable chap. Only the induction coil is a bit of a swine to repair in the EIS if it burns out but even that can be repaired.

You are correct. The EIS is the top of the control tree.

BTW - suggest you get yourself an OBDII scanner. A necessity with modern vehicles.

Russell Ormerod

CAN B will not affect Temp Gauge.

elphzwolf

Agreed, but a faulty EIS could not read it properly. The temp sensor cables give out a signal, hence the problem is further down, I think. Anyway, took it to the "local-electronics-guy-that's-supposed-to-fix-it" and he said he should have something by tomorrow... Guess I can just wait now

Glyn M Ruck

Please report what your guy finds. Mr Omerod's company in CT has a good reputation.

Russell Ormerod

Thank you-Glyn, appreciated.
well it will be interesting what your electronics guy finds always something new to learn with these complex electrical systems, just looking at the logic of it, the temp sensor is read by the engine controller and passed onto the CAN C network straight to the cluster and does not pass through the EIS. the fuel sender is read by the rear SAM and passed onto the CAN B network to the instrument cluster, usually when there is a network fault a lot of systems fail, E.G. No indicators no wipers no windows.

Glyn M Ruck

Did the dealer find CAN B & CAN C to be "STABLE" on Star?

elphzwolf

@Russell Ormerod no offense intended , just using my (obviously faulty) logic. @ Glyn thx for the diagrams. The dealers fount the CAN C to be stable, and could not read CAN B via the Star diagnostics. The voltage on the CAN B was off - 11V. The replaced the thermostat, and allegedly checked the coolant temp sensor and said that the sensor itself transmists a signal

elphzwolf

Update: went to the shop and saw the w203 disemboweled :/ They reprogrammed the rear SAM and got the fuel gauge working... The CAN B voltage is still off (11V) and they can't scan anything via ODBII wired on the CAN B behind the EIS. Turns out a few other things that were wrong before are somehow linked to this:

a) SRS alarm is on
b) RF remote key not working. IR is working fine, but at close range. I was initially led to believe that that they key was faulty, but turns out the key is fine

The guy's now off to disassemble the EIS. Fingers crossed

Glyn M Ruck

The RF remote operates through the same antenna in the rear screen as your radio. Does your car have a metallic tint? This is the common cause of RF problems. Another cause is water from applying tint to the rear screen shorting the antenna amplifier in the RHS rear C pillar Or when trimming tint they cut the wires where they exit the screen. There is also a sticky pad under the headlining centre of rear screen that comes unstuck. What is your AM radio reception like?

I will find you one of my previous threads in this regard with diagrams.

Key batteries do operate the RF link. For ignition & recognition the key is energised inductively by the EIS.

If CAN B is not stable it's usually a wire off somewhere. I'm sure your guy will sort that.

Glyn M Ruck

https://mbworld.org/forums/c-class-w...RF+Key+working

elphzwolf

Thanks heaps! The radio seems to be working fine on FM (hadn't tested it on AM reception, but I'm guessing they're using the same apm&antenna, so with that premise, the hardware should be ok). There is no tint on the rear windows. The main problem is that the CAN B cannot be accessed by the star diagnostics software.

Glyn M Ruck

OK - Yes FM/AM antenna is the same. The antenna amp might have failed. It's been redesigned multiple times. The RF side of the key might also have failed & only the IR is working. Do you have a spare to check with.

elphzwolf

No... Spare seems to be dead (no led flashing when buttons are pressed, even on new batteries), but the key was checked and the RF side transmits a signal (or so the guy said) will work more on this as soon as they get the mf CAN B to read via ODBII

elphzwolf

One more thing: could you please tell me the location of the N93 (the CGW which is supposed to be the connection between the ODBII diagnostic connector on the CAN D and the CAN B network) since the CAN B obviously retained its functionality i.e. i can close and open all the windows from the driver door hence there is some communication over the CAN B, even though i cant access it via the ODBII?

Russell Ormerod

Interesting, so your fuel gauge was a coding problem?
someone must of changed your rear SAM then. There are 2 fuel sender versions MAPPS and STD. rear SAM needs to know the difference.

Now getting back to your CAN B. Are you sure your car is fitted with a gateway module (N93) I have my doubts. meaning your EIS is the gateway. So from what you say your windows still function so your bus is still functional. but it is most likely operating in single wire mode. check the physical bus wiring for shorts to ground or to positive. I assume you can communicate to EIS but no body bus systems. then you need to look in actual values CAN BUS to see if CAN B is stable. Have a look at your diagnostic connector if PIN 1 is used EIS is gateway if pin 6 and 14 are occupied STAR will communicate via CAN D to N93 which is a small gray box fitted under the dash panel near your diagnostic connector.

elphzwolf

Thanks for your (more than helpful) input.

Correct. The rear SAM was replaced, but the new module was not "told" what the tank or the fuel sender was, so that was sorted out... As far as I know all pre-December 2004 C class cars are fitted with a N93 CGW, with the EIS taking over the functionality as of 2005, but I will check it out tomorrow when I go to the garage. As far as the CAN BUS goes, is it ok if I use an oscilloscope on it so that I can tell if the voltages and the pulses are OK according to the manual since I cant access it via STAR (and is that what you meant when you said "look up actual CAN BUS values")?

Glyn M Ruck

11 volts is correct for dormant & 4.65 for active.



If they can't get CAN B "stable" it's generally a wire off or to ground.

Just for clarification. MAPPS (magnetic passive position sensor) sensors were introduced 10/2001 on W203. Newer MAPPS sensors seam to align with US facelift end 2004. As you are aware the SAM's need to be coded accordingly or appropriate sensors fitted. This can be an issue when fitting new clusters to old cars or retro fitting Comand. (or of course SAM replacement)

A 2001 car should have N93 unless modified & has a new EIS.

Russell Ormerod

Check your CAN using a multimeter its good enough to check voltages.
Just do me a favour please. Connect Star, Establish comms with EIS read fault codes. or better do a short test for me and post it here please.

Glyn M Ruck

+1

elphzwolf

Update: Problem solved! They tried a replacement EIS and everything works like a charm. Right now the electronics guy is fixing my faulty EIS (if that's at all possible)... If not I'll be fitted with a new EIS. With the replacement EIS in place, I can read the CAN over the ODBII port, all the CANs are stable, fuel and temp gauges working, RF remote unlock working, SRS warning light gone, and I can access every module with the diagnostic software.

Thanks to both of you for all of your valuable input

So long (for now)...

Glyn M Ruck

Excellent news! - Damn EIS. I'm sure he can repair the EIS. They are stupidly priced for what they are.



Excuse highlight on induction coil.