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My 2002 W210 E320 4Matic's engine has problem starting. The engine was working beautifully, then 2 days after being parked, the problem happened. Here are some details:
I am quite sure it's not a problem with the security system/electronic steering lock - when I put the key in, the steering lock unlocks, and I can turn the key. So the key was recognized by the security system.
The engine would rotate perhaps 1/2 a turn, then it stopped. I tried it again after pulling the key out, same thing happened.
When the key was turned to position 2, I can see the gear selector showing P on the instrument cluster, and all the usual dash lights came on (for bulb check). I've tried to move the selector to N (which also shows on the instrument cluster) and tried turning the key, still 1/2 turn of cranking. I believe this shows that the TCU is able to communicate on the CAN bus?
There's fuel in the fuel rail - fuel was spraying out under high pressure when I pressed on the schrader valve on the connector for the fuel pressure tester, although I don't have a fuel pressure tester to test fuel pressure. The fuel pump and fuel filter were changed about 2 years ago, with original MB parts.
I always let the fuel pump prime before turning the key to position 3 to start the engine, and I can very clearly hear the fuel pump prime. So fuel pump should be good, and fuel pump relay should be good too.
There is about 1/4 tank of fuel left in fuel tank.
Found transmission fluid in the TCU, cleaned up that mess with electrical contact cleaner, as well as changed the connector at the transmission. Engine would still only rotate 1/2 turn, but still won't start.
Removed starter relay from the K40, and put a jumper wire between terminal 30 and 87 on the location for the starter relay on the K40. The starter kept running and the engine kept rotating when key is in position 2, which means the starter is good, and the engine is not seized.
The crankshaft position sensor was changed with a Bosch part about 4 years ago, and as mentioned above, the car was running beautifully before it was parked for 2 days recently.
Found a good deal on a new Bosch starter and installed it. After all, the starter was the original one, which is over 22 years old. Engine still wouldn't start - again only 1/2 a turn of cranking.
Scanned for code with a generic scanner, no codes at all.
Tested all fuses on K40 relay - all good. They all have 12V on both sides when key is in position 2.
Tested all fuses on driver's side engine compartment, driver's side dash, as well as under the rear seat. No bad fuses.
So, it seems like the 1/2 turn engine cranking was due to the ECU cutting signal to the starter relay, which stopped the cranking.
My guess is that the ECU saw the engine didn't start/fire up after the 1/2 turn cranking, and therefore, stopped the signal to the starter relay to prevent further cranking. Or maybe all the conditions necessary for engine start are not satisfied and the ECU stopped the signal to the starter relay?
My questions are:
1) What else can I can try or test?
2) Would a bad ignition coil cause this (I would imagine not, as I have seen engines running with one bad coil)?
3) How about a bad K40 relay? Anyway to test it?
4) Would a TCU be reporting "P" or "N" to the CAN bus for the instrument cluster to display, but report something else to the ECU?
5) Is there another mechanism for the ECU to determine whether the transmission is in "P" or "N"?
Unfortunately, I don't have access to Star Diagnostics, so I won't be able to check for the "Drive (or Start?) Enabled" status.
Any other advice would be much appreciated! Thank you in advance.
The battery voltage was around 12.8V. When I put the jumper wire between terminal 30 and 87 on the starter relay socket on the K40, the engine cranked very strongly when the key was in position 2, but the engine didn't start.
Originally Posted by Plutoe
1) there are just too many topics so my first repeat first question is what is the battery voltage
2) no
3) possible but your starter relay is good
4) if so you would never be able to move key
5) see 4 as you would never be able to crank
With very limited knowledge about our beloved MB E-class, I may be wrong but how old is the battery? Does it pass the cranking amp test? If you don't have battery tester, you can take them to most of the automotive parts store and they can check it for you. I really doubt that our MB will have problem with this, but worth checking as I work as GSE mechanic and most of the time when this happens, it's a weak battery. It may pass the voltage test, but may not have enough cranking amp. And yes, when you jump the starter relay, it will crank as you are bypassing the relay. Those big trucks have computer on-board and sometimes, it will not crank when you have too weak of a battery.
Once again, I could be wrong but to check the battery is free at almost all parts store, including NAPA ( at least around my areas are).
The battery is about 2 years old and it passed the load/cranking amp test. As mentioned before, the engine started and ran beautifully before it was parked for 2 days.
Any other suggestions? Thanks.
Originally Posted by ilove190evo
With very limited knowledge about our beloved MB E-class, I may be wrong but how old is the battery? Does it pass the cranking amp test? If you don't have battery tester, you can take them to most of the automotive parts store and they can check it for you. I really doubt that our MB will have problem with this, but worth checking as I work as GSE mechanic and most of the time when this happens, it's a weak battery. It may pass the voltage test, but may not have enough cranking amp. And yes, when you jump the starter relay, it will crank as you are bypassing the relay. Those big trucks have computer on-board and sometimes, it will not crank when you have too weak of a battery.
Once again, I could be wrong but to check the battery is free at almost all parts store, including NAPA ( at least around my areas are).
Same thing happened to my 2001 E320 it's funny cause not even Mercedes could not diagnose the issue but I finally found a guy online that had the same issue as well.
Here is what happened the K40 module cause a short which burned out the CPU fan in the very bottom of the black box once the fan goes the engine will either turn once or blow a fuse in the K40. After I replaced both the Fan & K40 car worked as new. The parts are extremely hard to find let me know if you can't I ended up buying two sets of each I have two E320's I might be willing to part with one.
I can hear the fan for ECU spinning when key is in position 2, so I doubt it's a problem with the fan. I have also tried to unplug the fan from the K40, and the engine still wouldn't start. As mentioned before, all the fuses on the K40 are good, and has 12V on both sides when key is in position 2.
Is there a definitive way to test the K40, other than replacing it with a known good one?
I said exactly what you said I thought I could hear the ECU fan but its made to be silent and I also unplugged the fan still nothing I thought I was the one who had to be wrong but again after I replaced the parts it started up. The working fan completes the circuit I had the option of taking the K40 out of the other car I have and it still would not work. I had people tell me try a tissue paper test or smoke test to see if the fan is blowing still nothing. The fan itself is connected to the firewall where the inside blower also seems to assist the circulation of air. I personally thought that there is no way that little fan stops a car from working but it does and its really dumb.
If you are able to buy both new or used you should so many hours have been $$pent try diagnose 99-02 W210 cars when it turns out to be that simple. Let me know if you get this done..
1) if the fan is unplugged, and all the K40 fuses are good, the engine not starting is a sign of a bad K40 (assuming everything else checks out as mentioned in my original post)?
2) With a known good K40, a bad fan will stop the engine from starting, even if the K40 fuses are not blown by the bad fan?
In other words, both the K40 and the fan must be replaced to solve this engine not starting problem?
Thank you in advance!
Originally Posted by AllanP
I said exactly what you said I thought I could hear the ECU fan but its made to be silent and I also unplugged the fan still nothing I thought I was the one who had to be wrong but again after I replaced the parts it started up. The working fan completes the circuit I had the option of taking the K40 out of the other car I have and it still would not work. I had people tell me try a tissue paper test or smoke test to see if the fan is blowing still nothing. The fan itself is connected to the firewall where the inside blower also seems to assist the circulation of air. I personally thought that there is no way that little fan stops a car from working but it does and its really dumb.
If you are able to buy both new or used you should so many hours have been $$pent try diagnose 99-02 W210 cars when it turns out to be that simple. Let me know if you get this done..
Yes, that is correct.
Many people suggest with a bad K40 to solder it however if you do not put it in a known working car to know 100% that the broken solder joint was the issue then it is still a guessing game.
Example I recently had my pollution control sensor go on the car and it threw a code for that however it was not that sensor that was the problem it was the temp control sensor on top of the dryer for the A/C and the sun sensor that were causing a chain reaction, took the pollution control sensor off another working car. I replaced the sun sensor and temp control sensor which are way cheaper than the pollution control sensor put back the original P/C sensor all works good, so even if you have a good quality MB Autel code reader sometimes these cars are getting old and electrical parts are getting scarce it does not hurt to have a spare transmission control unit spare. Cars with electronic components do need to be replaced. BTW I just had my right front CV go without warning on the 4matic which has caused the transmission not to go into park ??
I hate to be the azz to be telling you this, but it's your car, brother. What you want to do is completely up to you. If no one can help you here, then it's time to take it to professional. Call them to come to your place or to get it tow, that's another decision you have to make. If your car not worth towing or have it seen by mechanic, then it's time to sell it.
One last ditch effort, maybe ask one of the member here that's living relatively close to you can have them look at your car? Maybe for a pizza and beer or for a small fee?
I thought this forum is about helping each other learn and work on their older W210 Mercedes. If the solution is to just call a mechanic, then why do we need a forum like this? As far as I can tell, most of us here keep an older Mercedes like the W210 not because we cannot afford newer cars (not just MBs), but rather, it is our love for the W210 that we gather in this forum.
The W210 is not my daily driver, and I like to work on it when I have time. I am a W210 enthusiast and committed to getting it running again, with the help of my fellow W210 owners in this forum.
ilove190evo, you asked me to make decisions. In case you missed it, I believe my decision has been very clear and obvious from the beginning - my decision is to fix the car myself and get it running. If your only suggestion is to tell me to find someone else to fix the car, then you are really missing the point of this forum. I know you are a mechanic as you mentioned in a previous post, and you could be biased against DIYers, because DIYers are not professionals like you. Your time is valuable because you are a professional. However, with the time it took you to type your message, you could have given me your professional suggestions (assuming you want to be helpful) on what else to check/try on my car.
Update: I believe I have traced the starting problem to a bad ground, specifically, wire 9 (brown) of the harness for the B1 connector (10 pin) on the K40 relay. Wire 9 (brown) is supposed to be connected to ground, according to the circuit diagram.
However, I found that there's no continuity between ground and that brown wire.
To double check, would any one be kind enough to check their harness for the B1 connector on the K40 relay to confirm that there is continuity between ground and the brown wire?
Pin 9 should be connected to ground but it should not prevent the relay from activating the starter motor solenoid. Pin 9 circuit has the diode in it to stop the EMF backlash when the starter relay opens and the electric field in the starter motor solenoid collapses. At the same time, you should be able to just wire in a new ground without damage to the circuitry.
Pin 1 or 2 should have 12 volts on it (I don't know which) and the other pin should be an open-collector pull-to-ground initiated in the ME control module.
Do you have continuity from pin 6 (violet) to the starter motor solenoid? Have you tried disconnecting the violet wire from the starter motor solenoid and directly applying 12 volts to the starter motor solenoid?
Also, you can purchase a "relay bypass switch" with which you can bypass the relay with a manual on/off switch. This would be my first step. Naturally, don't switch it on and walk away...
If you have 12 volts on pin 3 and continuity from pin 6 to the starter motor solenoid, I would say it is either a bad starter relay, a bad starter motor solenoid, or the Motor Electronics is not activating the relay. Confirm continuity from pin 1 to the ME and pin 2 to the ME.
Last edited by bbirdwell; Apr 3, 2025 at 10:12 AM.
Thanks for your reply. I will try to add a new ground for pin 9 later.
I did pull out the starter relay, and jumped terminals 30 and 87 for the starter relay on the K40, essentially creating a starter relay bypass. When the key was turned to position 2, the starter turned the engine perfectly (I disconnected the fuel pump relay to prevent the engine from firing up). So, it looks like all connections from the K40 to the starter motor solenoid are all good, and the starter and starter solenoid are all good?
I've also tried a known working starter relay, but still had the same problem. The starter relay did click and engage, which caused the starter motor to turn the engine about 1/4 turn. The starter relay then disengaged. If I hold the key in position 3, the starter would turn the engine 1/4 turn, then stop, then another 1/4 turn, then stop. The most I have gotten was 4 of these "cycles" by holding the key in position 3. After that, these 1/4 turn "cranking" will stop completely.
I really hope it's not the case, but does this sound like a problem with the ECU?
Not sure yet about the ECU but could it be caused by a "no signal" condition from the crankshaft position sensor? I do not definitely know but perhaps the ME disengages if it fails to receive a signal that the flywheel is turning?
Could the starter itself not have sufficient torque to rotate the crankshaft? Possible bad starter or undervoltage condition?
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