PCM Question

I am a new comer to this webpage but frequent the www.thedieselstop.com page
I am the founder of www.houstonareapowerstrokes.com with a question for the Lincoln Mark VIII experts.

I (wife's) have a 97 Mark VIII. When putting it in Drive, it displays an error message of "gear display error" ( P0705 ). Its OK in Park, Reverse and Neutral. But when it going into Drive, the error message is displayed and the error code is thrown. I have replaced the part on the side of the tranny that moves with the shifter with no luck.
The dealer today said the PCM is not communicating with the Tranny.
I'm not sure this is correct. Its OK in Park, Reverse and Neutral but when it hits Drive the error message is displayed. This has been going on for months. The only time I can feel a differance is when the car is slowing down for a stop, I can feel the tranny shifting down from 3rd to 2nd or from 2nd to 1st.

My Question is, before I replace the PCM, can this be a logical problem. The PCM is OK in Park, Reverse and Neutral but, have a problem when in Drive. I will get the car back tomorrow and will be able to tell the PCM code.

Does anybody have any suggestions?

Thanks

RE: PCM Question

Maybe I looked up the wrong thing but from what you posted the PCM is never mentioned as needing replacement in the trouble shooting portion of the manual.

Need the codes it throws.

RE: PCM Question

A Bill

This is part of my concern. The code it throws is P0705.

I have a chip burner and was wondering if I installed
a chip if it might clear up the problem.

Thanks for your input.
Any more ideas???

RE: PCM Question

I (wife's) have a 97 Mark VIII. When putting it in Drive, it displays an error message of "gear display error" ( P0705 ). Its OK in Park, Reverse and Neutral. But when it going into Drive, the error message is displayed and the error code is thrown. I have replaced the part on the side of the tranny that moves with the shifter with no luck.
The dealer today said the PCM is not communicating with the Tranny.
I'm not sure this is correct. Its OK in Park, Reverse and Neutral but when it hits Drive the error message is displayed. This has been going on for months. The only time I can feel a differance is when the car is slowing down for a stop, I can feel the tranny shifting down from 3rd to 2nd or from 2nd to 1st.

Click to expand...

Was "the part on the side of the tranny that moves with the shifter" called the MLPS(Manual Lever Position Sensor)?

IMO if "The dealer today said the PCM is not communicating with the Tranny." was true, you wouldn't be going far since the transmission is an electronic shift transmission.

My WAG is the harness connector(s) to the shift solenoids has a poor connection... that's where I would start looking. The MLPS change(if that's what it was) was a good effort, and in fact there may be a harness connector problem there.

I'm actually guessing since I don't have a Gen2('97-'98) - my limited experience is with my '93 Gen1('93-'96).

BTW, welcome and ... PowerStrokes rule!
(Right after Mark VIII's of course!!)

RE: PCM Question

Yes, The MLPS is what I changed out. It was only about $50, so I didn't feel like I was going to waste much money if I gave it a try.

What I don't feel comfortable about is: Is the PCM communicating in Park, Reverse and Neutral? But not in Drive. I would think it would communicate or not communicate. Not just in certain gears.



***************
BTW, welcome and ... PowerStrokes rule!
(Right after Mark VIII's of course!!)
***************

Thanks for the welcome.
My PSD is quicker (1/4 mile times) and gets just about the same MPG as the wife's stock Mark.

RE: PCM Question

I still doubt the PCM is the problem, particularly since it hardly seems to have an drivability issue. The MLPS could still be suspect.

>What I don't feel comfortable about is: Is the PCM communicating in
>Park, Reverse and Neutral? But not in Drive. I would think it would
>communicate or not communicate. Not just in certain gears.

Excerpts from AllData:

The Manual Lever Position (MLP) sensor provides an input signal to the Powertrain Control Module (PCM) , notifying the PCM of the current transmission shift lever position.

CONSTRUCTION
The MLP has six separate resistors in series. Each resistor has an output connection corresponding to a transmission position (P, R, N, D, 1, 2). The output wiper arm is linked directly to the transmisssion selector linkage.

OPERATION
The PCM applies a 5.0 volt reference signal to the MLP circuit pin 30. SIG RTN circuit pin 46 supplies a ground path to the sensor. As the transmission is shifted the MLP output wiper arm moves to a corresponding resistor connection. The six inline resistors provide a separate voltage drop for each transmission position.

It could be the MLPS is not sending the correct signal to the PCM when in drive. I look at it as descibing your problem as the MLPS is not communicating with the PCM.

Troubleshooting steps relative to this includes the harness connectors at the MLPS and PCM, checking for damaged or pushed out pins, corrosion, loose wires, etc..., adjustment of the MLPS, checking the circuit for shorts to power or ground and checking sensor resistance.

I would suppose the condition could also be caused by harness or connector problems at the shift solenoids as well.

RE: PCM Question

OK, I was looking at the wrong thing.

P0750 Shift Solenoid No. 1 circuit

SS1 circuit failed to provide voltage drop across solenoid. Circuit open or shorted or PCM driver failure during on-board diagnostic.

Unfortunately you need to hook up an NGS to go through the proper troubleshooting sequence. It starts with the transmission connector and goes from there. Sorry it is of no help.

RE: PCM Question

Driller

Thanks for the info. I agree with you, I don't think the PCM is the problem. I will check connections before I commit to a new PCM.