Well after buying a new meter due to the failure of my old one. I am not sure if this is good news or not. the power at fuse 33 is fine

 

Something I noticed this evening when I put the lights on it. The J gate does light up the white symbols. It just doesn't turn red when I move the selector

 

Two distinct circuits at work here.

A single symbol will illuminate red, based on feedback from the TCM, to indicate whichever gear is engaged at the transmission. This light is fixed brightness.

The remaining symbols will illuminate white. The brightness varies with the dimmer switch for the dash and console lights.

So it's good the white symbols are working, but it doesn't change the fact you're still not seeing the feedback from the TCM.

Remember it's easy to panic and convince yourself the TCM has failed, but it's far more likely to be an external problem such as wiring, etc. So far you've only done the simple stuff such as checking fuses. It's probably time to get a little more involved and check for power and ground where the vehicle harness connects to the transmission. Not a lot of fun, and access is difficult underneath the vehicle.

 

While tinkering around with the car today I discovered something very strange. R20 the stater relay in the engine area has one constant live and one switched live from the ignition switch. The other two conections are negative until I turn the ignition key where upon the one that is suppost to stay negative becomes positive. If I than add a negative supply to it the engine turns over. This is with the relay in place but with a wire sticking out attached to what should be the negative supply from the ECU. This car is driving me NUTS!!! If I had a can of petrol handy I would have set fire to it today!!!! Thankyou Karl for your input. I had planned on getting under the car today, but my drive on ramps are too sharper angle to allow the front spoiller to clear them. I am also waiting for a knee replacement so I am not as agile as I used to be. I will have another go at getting under the car tomorrow. So fingers crossed its a bad conection at the gearbox.

 

One last thought before you crawl under the car. Kind of a longshot, but this potential problem is quick to rule out.

The fuseholders on these cars have sometimes been found loose, not gripping the fuse blades very well. To test, cut a spare fuse in half so it only has one blade. This will be used to test the grip at the fuse panel. Remove any suspect fuses (as previously listed) and try your test piece on each side where the fuse fits. You may need to use a small pair of needlenose pliers. Don't use a whole fuse, as this won't reveal if only one side is loose.

Don't get your hopes up too high, but who knows. Should only take a few minutes to try.

 

Thankyou again Karl for another good idea. I did a check on all the fuse conections and they are good. I manage to get the car on my small ramps today and slide under it. There looks to be a small film of oil on the gearbox sump. I am now wondering wether it may be suffering from the same problem a lot of Mercs suffer with. Transmission oil in the TCM plug connector. All the symptoms are basically the same.After watching a couple of youtube videos I now know the the rear gearbox support needs removing to access the plug. I now need to find someone with a four poster ramp I can use for an hour and pull it apart.

 

Good thing to check, but until now I had been concentrating on external issues. Were others also.experiencing the same lack of indicator lights and no.comm with the.TCM? With oil in the sleeve, I thought the main symptoms were mostly shifting problems, not a failure to start.

 

+1

I can't see why it would fail to start for anything related to that.

I think therevday is looking in the wrong place.

 

Thanks guys for your thoughts. My train of thought ( though this may be completely wrong} is if the car cannot see the TCM due to oil in the plug. Then it will not know where the trainsmission lever is. Thus not sending an ok signal to the ECU Hence the no start I may be barking up the wrong tree. Something is stopping the TCM from comunicating with everything.I have voltage at all the important fuses. Though why I have + at the starter relay when it is supposed to be a - signal on the switching side is very strange. I need to get the car up in the air even to check the plug for continuity.

 

What happened about post #9? The 2 bolts are critical.

 

What tool is it? Many do not work properly.

 

The two bolts are tight. My scanner is a Snap on Ethos. It comunicates with every other function ABS Engine, Air Bags but as soon as I try to comuncate with Transmission it comes back with no comunication. It also told me that there is no comunication between the ABS and the TCM or the ECU and the TCM

 

It's possible it simply does not support the TCM in the car.

 

Strictly a guess, but this may be normal. For a normal start scenario, the ECU supplies the ground to energize the starter relay. But at any other time, perhaps this leg is switched positive, not just switched off as you might expect. It won't hurt the starter relay's control coil to have power on both sides. No voltage difference, thus it won't energize.

Another possibility is your meter may be picking up very weak stray voltage through the ECU. You'd only read this in an unloaded circuit, and it basically means nothing. Digital meters can be overly sensitive to this phenomenon.

 

+1 on that. I work with broadly comparable systems in aviation. When I encounter test results that make little sense, I've learned to always consider a problem with the test equipment. This has saved me lots of grief on several occasions.

Any way you could borrow a different brand scanner?

 

IDS/SDD ...

 

Yesterday I had the the car plugged in at a garage near me. There test equipment could not comunicate with the TCM. The plug for the TCM was removed. It did have oil in it. I cleaned both parts out with electrical cleaner. Reconected but no difference. It is almost as if the TCM is not there.I am now considering buying another gearbox to stick in it just to prove my TCM is knackered!!!

 

Can't stop you, but that is some very expensive and labor-intensive troubleshooting. Yikes!!!

Have you checked yet for power and ground where the vehicle harness connects to the transmission? How about continuity on the wire pair for the data bus? In my over-inflated opinion, you are WAY more likely to have a simple external fault (such as a wire melted to an exhaust pipe) versus a very rare total failure of a computer.

Other than that, I don't know what to suggest.