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Have 2004 e55 amg, the car will engage starter, crank for 1/4 sec then stops. Car starts normal with tcm disconnected. Got used tcm and same thing. Took transmission valve body down and inspected and checked neutral, park conductivity, 900 ohms, while in rev or drive. Park and neutral is open or infinity ohms. I checked all the way up the cable to tcm. Checked the wire loom for broken wires, resistance and shorted out wires. The only confusing thing is that the can+ and can- seems shorted while connected to the trans. Yes the ohms are low for the relays when connected to trans as it should. So here is the question, what in the trans besides neutral safety could cause start cancel?
Battery load tested checked good 12.5v
Terminal wires checked from battery to passenger SAM
Starter wire and lugs checked from starter to SAM
Front SAM took apart and checked all fuses, connections
Starter relay replaced
Starter replaced
TCU replaced
No DTC codes
No ODB2 codes
Car starts just fine with TCM or transmission round wire connector removed!
Purchased MBII scanner.
Battery load tested checked good 12.5v
Terminal wires checked from battery to passenger SAM
Starter wire and lugs checked from starter to SAM
Front SAM took apart and checked all fuses, connections
Starter relay replaced
Starter replaced
TCU replaced
No DTC codes
No ODB2 codes
Wires checked from transmission to TCU for shots, opens
Car starts just fine with TCM or transmission round wire connector removed! I been pulling my hair out for the past 60 days, anyone has anymore ideas. I seem to run dry of searches on the web,
Last edited by pasta; 11-18-2019 at 04:18 PM.
Reason: add more info
When I replaced my TCU with a used tuned one I had starting issue until I did sneaky transmission reset proceedure. Aka put key in position 2 keep foot flat for 5-10 seconds, turn key to off position but leave in for 2+ mins... pull key out for a bit then turn car on fingers crossed.
Prob not your issue and u mightve tried but u asked for ideas..hehe
If you have not done this you should have someone diagnose it. If you hook up to it with Star it will show if it is in P/N. All sorts of helpful information to diagnose the problem rather than shotgunning parts at it. It could be as simple as the linkage is out of adjustment.
I have the MBII scanner, while it is not the STAR, it does good part of the diagnosis. I did find out that now that I don't have any DTC or ODB2 error, i am in need of one. ANYONE near SLC willing to give a hand? I can come to you?
I am a software engineer, mechanic on the side for the last 40 years. If my perception of MB dealer is correct, this fix could be at least couple grand. From what I read on this forums, they follow the star recommendation to the tee. This means that they will start at ground zero, and after min of 2000 in fixes, the issue can still exist. I dislike the dealers with a vengeance. It is a money pit, especially when they see an $80k vehicle that is 15 years old.
i done all ground work, and to pay them 130/hr it kills me. All the dealership focuses on next sale, maintenance of vehicle under warranty.. when they get a car like this, this is the gravy train. They will milk me for every penny to teach me to have a car less than 5 years old.
Ok, Does your scanner show in the TCM data stream if it is in Park or N etc. OBD codes can be generic and only be engine codes. Your issue may not be a fault code but rather an incorrectly reading N/S value. When you unplug the TCM the ecu gets N/S from the Shifter. But when the TCM is plugged in the ecu looks at a specific BIT in the TCM data for N/S. This should be as you have discovered a combination of the lever position and the open circuit of the fluid temp sensor when in P and N. These need to match.
As far as dealerhips go. There are good ones and bad ones. And at each there are good technicians and bad ones. But one thing is for sure you do not have to do any of the recommend repairs and in fact you can just tell them up front that you do not want them to do anything but diagnose the issue. You have to authorize repairs and diagnosis. But this should be pretty easy.
I get the "dealerships suck" thing, but as noted above you can have them just do the diagnostics. Almost guaranteed to be cheaper than shotgunning parts...
What does the ecu show for permission to start? It has values for DAS release and n/s that you can read as well. Do these values change after trying to start the car?
Took it in to SLC stealership! The mechanic spend 5 hr with computers and all and could not find the issue. Feeling lucky that I spent only $350, i ran as fast as i could when they mentioned that they need 7 more hours to troubleshoot the transmission. The transmission is somehow sending signal after start atempt that the transmission is in gear. The conductor plate was replaced about 6 months ago with an aftermarket one in order to solve the no crank issue back then. The TCM was swapped out for a min in order to make sure it was not the issue. Th TCM needs to be programmed to the transmission valve body in order to leave this replacement in the car. I replaced it back with the original one. I did open it and noticed a little bit of oil on the board. I clean it with alcohol and can of air then installed it back in the car.
I am back to ground 0 almost, i do have one clue that with the TCM disconnected the car starts like it should. When the TCM is connected the car starter clicks and that is it. Need to cycle the key and move the shifter from park to any gear and return back to park or neutral in order to click again. Something in transmission is making the TCU think that the transmission is in gear 1/10 of a sec (hence the starter click, then cancel).
I am ordering a MB conductor plate, even thou I fell that will not solve the issue.
Conductor is pretty easy and cheap at this point and could be very well your issue....even though you spent to much already with no resolution unfortunately.
I am not 100 percent sure but I did not think you have to program anything to put in a new TCU.... but if you found oil on the TCU wires then it wicked up from the transmission bulkhead electrical connector,, try disconnecting that plug at the trans and start (sounds like you need a new one of those connectors anyway - they are inexpensive) ? -- also you said it starts with the TCU disconnected, can you plug it back in while its running and see if it continues to run/drive ? good luck
Yes, i did replace connector at same time i did the conductor plate. Yes the car continues to run once started with TCM plugged in. I guess i could find signal wire from trans that causes start cancel, place a switch in, turn switch off to start car then turn on once started. The issue is that the trans tells the starter to cancel (hence click only)
If you have not check your engine ground strap. I do not think this is it but I would check it anyways.
What you are describing is very odd. Check the shifter linkage adjustment. That you are having to cycle the shifter in and out of P after a start attempt makes me feel like something is moving when trying to start the car. The only N/S function in the transmission is the Temp sensor goes open circuit in P and N so having the trans unplugged.
What did the dealership say? Did they have fault codes?
This really should not be hard. There are only 3 things related to the transmission. The Shifter, the tcm, and temp sensor on the conductor plate. That is it. You should be able to start the car with just plugging in the conductor plate and pushung the button in by the temp sensor.
The dealership stated that they never ever seen a car with this issue. Everything checks out, everything is good, start authorization .... Once the start is initiated and the starter clicks, something is sending a start cancel to the CAN and the starter is disabled. What is weird is the fact that the transmission shifter has to be moved, to try to start again. Yes the key has to be cycled also in order to get the start authorization, but the sifter movement is the concerning part. I guess I can take off the shifter connector and see if the car starts with TCM plugged in! Maybe the issue is not in the trans and it is in the shifter sensor maybe the start cancel is recived from that. I just don't get it why it does not check that first, but after the start is initiated.
Y3/6s1 in the transmission. Starter lockout consists of a plunger, permanent magnet, and reed contact. Located in the electrical control unit Y3/6 on the conductor plate and the lockout is permanently connected to the conductor tracks. The starter lockout contact's task is to recognize the selector valve and selector lever position "P" and "N". Bottom Line Up Front: if the reed switch is closed, no start. Reed switch open, start. You should be able to verify this by pulling removing pin 34 from the harness connector at the TCM (more info below).
Y3/6 is located on the conductor plate on the opposite diagonal corner from the electrical connector.
Pin 4 on the vehicle harness connector carries the transmission fluid temperature plus the P/N switch signal. Color code is green and the opposite end is pin 34 on the TCM. Pin 33 on the TCM (pin 12 on the transmission electrical harness connector) is the ground for the speed sensors, TFT sensor, and the Park/Neutral reed switch (i.e. all share a common ground)
The reed switch is closed only when the gear shift is in the reverse or forward gear position (ATF temperature monitoring is enabled). This implies the reed switch must be open in Park or Neutral. When in "P" or "N" the contact is actuated by the inside detent plate which moves the permanent magnet away from the dry-reed contact. The dry-reed contact opens, and the TCM closes the signal to the starter circuit.
I do not know what activates/moves the plunger for the starter lockout. Possibility the problem exists here. WIS shows an adjustable linkage at the shifter end of the transmission shift rod under the car. Perhaps the shift rod is not pulling the transmission selector lever on the side of the transmission to the proper position. Adjustment is unscrew/loosen set screw from head (located on bottom end of shift lever under the car. will require removal of the rear belly pan), move transmission selector lever on side of transmission all the way forward (D position) and the range selector lever (shift lever) to the D position, screw the set screw into the head 12 Nm.
Possible test: at pin 34 of the TCM, with shifter in R or D, you should see approximately 1.2 volts at 20*C or 1.3 volts at 30*C. With shifter in P or N, you should see no voltage but rather an open circuit. Alternatively, test for resistance; again at pin 34 of the TCM, you should see ~957 ohms at 20*C and ~1032 ohms at 30*C with shifter in R or D. With shifter in P or N, you should see open circuit.
Hope this helps you. If you don't have it, I recommend purchasing the ATSG 722.6 Service Manual. Best money I ever spent to understand these transmissions.
11-17-2019, 11:50 AM
