[Tejas Ingle]

Presently working on Mercedes-Benz C class. Since this is a research vehicle, its specs do not match the standard C class.
The problem is that it refuses to start. In position 3 of the key, (where the starter is deployed) there is absolutely no response from the car. The starter does not crank the engine at all.
I checked the battery, the fuse, the relay, the voltages at all these points, the ground connections and found everything to be OK. According to the wiring diagram, the ECU controls the starter relay. But this does not seem to be happening.
Any one has an idea about the problem? The star diagnosis tool is not available to diagnose the problem.

[wild child]

Originally Posted by Tejas Ingle

Presently working on Mercedes-Benz C class. Since this is a research vehicle, its specs do not match the standard C class.
The problem is that it refuses to start. In position 3 of the key, (where the starter is deployed) there is absolutely no response from the car. The starter does not crank the engine at all.
I checked the battery, the fuse, the relay, the voltages at all these points, the ground connections and found everything to be OK. According to the wiring diagram, the ECU controls the starter relay. But this does not seem to be happening.
Any one has an idea about the problem? The star diagnosis tool is not available to diagnose the problem.

replace the starter motor and try cranking her. if it still does not crank, connect the OBD tool and check for any sensor failure in the car.
anyways, how come you have a research car with you? u work for merc?
- wild child

[Tejas Ingle]

Originally Posted by wild child

replace the starter motor and try cranking her. if it still does not crank, connect the OBD tool and check for any sensor failure in the car.
anyways, how come you have a research car with you? u work for merc?
- wild child

I am under training with Diamler-Chrysler; so working on research car. The starter motor is OK, and has no problem. Also the connections are proper and there are no lose connections. OBD (STAR DIAGNOSIS) is not available to us.
When we turn the key to start the engine, the ECU controls the starter relay. That is not happening. I dont know why . The ECU controls the ground of the starter relay and switches it ON, which in turn supplies current to the starter motor.

[taranonline]

check the connections to gearbox.. if the wires to gearbox are not connected, these cars wont start. Learn't this in Australia.

Hope this helps.

[mayankk]

Originally Posted by Tejas Ingle

I am under training with Diamler-Chrysler; so working on research car. The starter motor is OK, and has no problem. Also the connections are proper and there are no lose connections. OBD (STAR DIAGNOSIS) is not available to us.
When we turn the key to start the engine, the ECU controls the starter relay. That is not happening. I dont know why . The ECU controls the ground of the starter relay and switches it ON, which in turn supplies current to the starter motor.

i wont be able to help, and neither do i want to because i am quite envious of you.


just a couple of things, though.
1. how did you land this?
2. when you say "research" car, and youre in training, isnt this cheating?

[wild child]

Originally Posted by Tejas Ingle

I am under training with Diamler-Chrysler; so working on research car. The starter motor is OK, and has no problem. Also the connections are proper and there are no lose connections. OBD (STAR DIAGNOSIS) is not available to us.
When we turn the key to start the engine, the ECU controls the starter relay. That is not happening. I dont know why . The ECU controls the ground of the starter relay and switches it ON, which in turn supplies current to the starter motor.

Why don't you diagnose her with the OBD tool?

even if she is a research beauty, she should have a software copy right?

[BeamerBoy]

You can do it the traditional way using the multimeter.

1 Once the ignition is on, check if the circuit from B+ to the earth is complete.

2 You may use the Amm clamp or the continuity tester to do that.

If you do not have a multimeter, you may use a crude bulb+fuse arrangement and wire it instead of the starter motor.

Eventually you will have 2 situations:

The circuit works/Bulb lights up/current flows => earth connection is corrcetly triggerred. Check starter motor or battery voltage.

The circuit does not work => Doubt the trigger/ECU/Relay/Sensor or wiring damage/loose connection to earth.

If you pm me the wiring diagram, perhaps I can have a look as well.

Trust this helps.

[Tejas Ingle]

Originally Posted by taranonline

check the connections to gearbox.. if the wires to gearbox are not connected, these cars wont start. Learn't this in Australia.

Hope this helps.

OK. I am studying the transmission wiring diagram at the moment.

Originally Posted by mayankk

i wont be able to help, and neither do i want to because i am quite envious of you.


just a couple of things, though.
1. how did you land this?
2. when you say "research" car, and youre in training, isnt this cheating?

We have the freedom to use all the available sources to solve it. The only condition is that it should be done logically. Besides, the problem isn't the part of our training. It just popped up.

Originally Posted by wild child

Why don't you diagnose her with the OBD tool?

even if she is a research beauty, she should have a software copy right?

We are not given the access to Star diagnosis tool yet as then it will do all the job and leave nothing for us.

Originally Posted by BeamerBoy

You can do it the traditional way using the multimeter.

1 Once the ignition is on, check if the circuit from B+ to the earth is complete.

2 You may use the Amm clamp or the continuity tester to do that.

If you do not have a multimeter, you may use a crude bulb+fuse arrangement and wire it instead of the starter motor.

Eventually you will have 2 situations:

The circuit works/Bulb lights up/current flows => earth connection is corrcetly triggerred. Check starter motor or battery voltage.

The circuit does not work => Doubt the trigger/ECU/Relay/Sensor or wiring damage/loose connection to earth.

If you pm me the wiring diagram, perhaps I can have a look as well.

Trust this helps.

We have all possible equipments and I have checked for all the continuities. There is no problem with any connections.
After all these investigations, my observation is that the relay is OK but is not being actuated by the ECU. Scratching my head since yesterday to figure out why is the ECU not obeying direct orders. No problem with the CAN network either since everything else is working. To me it looks like some parameter or the 'condition' of the ECU is not being fulfilled.

[Tejas@perioimpl]

Have you checked the transmission position? The car won't crank (no response) if it's in D or R. Check to see if it's in P or N.

It's happened to a friend who panicked and called me after wasting an hour trying to start his new merc.

[Tejas Ingle]

Originally Posted by Tejas@perioimpl

Have you checked the transmission position? The car won't crank (no response) if it's in D or R. Check to see if it's in P or N.

It's happened to a friend who panicked and called me after wasting an hour trying to start his new merc.

The car is in 'Park' mode.
Its unusual that the car was in D when he was trying to start it because the key cannot be removed from the ignition unless it is shifted to P. Or may be it is a push button start.

[Tejas@perioimpl]

Originally Posted by Tejas Ingle

The car is in 'Park' mode.

Then it's a problem with transmission i think. Check that.

[Tejas Ingle]

Originally Posted by Tejas@perioimpl

Then it's a problem with transmission i think. Check that.

Taran too pointed out towards the transmission. I checked the wiring diagrm related to transmission today. I will check the car again tomorrow.

[Xehaust]

You say you have checked the fuse. Which fuse did you check?
Try checking the fuse for the fuel system & check if it has any loose contact points. Let me know if this solves the issue

[Tejas Ingle]

Originally Posted by Xehaust

You say you have checked the fuse. Which fuse did you check?
Try checking the fuse for the fuel system & check if it has any loose contact points. Let me know if this solves the issue

I have checked the starter fuse which is Ok. I can hear the buzz of the fuel pump when I turn on the ignition which means that the fuel pump fuse is OK. Are you refering to some other fuse?

[Xehaust]

Well, had a random not starting issue in the C (although its the newer 204) and after several complaints & trips to the MB service centre, they finally diagnosed it as a loose contact on the "fuel system" fuse. Its been starting up perfectly ever since.

The problem seemed similar to what you have stated, everything used to look fine except that there used to be absolutely no response on turning the key. The lights used to come on, there would be no warning chime, everything seemed in perfect order. Just that when the key was turned, nothing No click sound, no ignition, no nothing