Transmission doesn't change the gears - limp mode?

Hello everyone, my name is Maciej and I'm from Warsaw, Poland. Some days ago I became an owner of 2 door 1997 Chevrolet Tahoe 6,5 TD 4WD. For a long time I've been looking for an 90s 4 door Suburban or Tahoe with gasoline engine, but one day I found this offer. :) It is a bit neglected and the guy who was selling it, stated that transmission is broken. Nevertheless I decided to buy it because it is almost rust-free, except 2 small points on body, it has nice interior and beside some malfunctions and a ton of dirt it is in a good shape. I bought it as a secondary car, just from passion for these ones.

OK, so the main problem is that transmission does not change the gears: the car can only drive at the 1st gear and reverse. "Check engine" and "ABS" lights at instrument cluster are on. I have the feeling that the problem is not in transmission itself, it looks more like the car is in a limp mode. After inspecting it, I have found some unplugged wire harnesses at the top of the engine - I have no idea where they should be plugged and why are they unconnected. I have also pulled out OBD codes (list below) and found nothing about the transmission, but there is a CAN communication error code - maybe scanner can't connect with transmission electronics? It is also strange that there is no ABS code.

I would like to ask you for help with identifying those unplugged harnesses, I will be very grateful for wiring diagrams and some overall tips for this engine. At first I will check/replace throttle position sensor and fuel shut-off solenoid, I must also plug those harnesses and see what happens then. I hope that PCM is OK, It would be hard to get.

Regards,

Maciej

Photos:

Attachment 6419Attachment 6420Attachment 6421

High resolution photos: https://imgur.com/a/0lSizrK

Codes:

Code:

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Car Scanner ELM OBD2
DTC report
Selected brand: Chevrolet

============1==============
P0601
Raw code: 0601
ECU: 10
Status: Pending
OBDII: Engine control module (ECM) - memory check sum error

============2==============
P0601
Raw code: 0601
ECU: 10
Status: Confirmed
OBDII: Engine control module (ECM) - memory check sum error

============3==============
U1000
Raw code: D000
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test is inhibited by other DTC, Test has not been completed, Validated fault present at time of request
OBDII: Class 2 Communication Malfunction

============4==============
P1218
Raw code: 1218
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Validated and stored in non volatile memory
OBDII: CID High
Chevrolet: Injection Pump Calibration Circuit

============5==============
P0601
Raw code: 0601
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Engine control module (ECM) - memory check sum error

============6==============
P0228
Raw code: 0228
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Throttle position (TP) sensor C/accelerator pedal position (APP) sensor C - high input

============7==============
P0223
Raw code: 0223
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Throttle position (TP) sensor B/accelerator pedal position (APP) sensor B - high input

============8==============
P0215
Raw code: 0215
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request
OBDII: Fuel shut-off solenoid - circuit malfunction

============9==============
P0122
Raw code: 0122
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Throttle position (TP) switch A/accelerator pedal position (APP) switch A - low input

============10==============
P0601
Raw code: 0601
ECU: 10
Status: Pending
OBDII: Engine control module (ECM) - memory check sum error

============11==============
P0601
Raw code: 0601
ECU: 10
Status: Confirmed
OBDII: Engine control module (ECM) - memory check sum error

============12==============
P0601
Raw code: 0601
ECU: 10
Status: Pending
OBDII: Engine control module (ECM) - memory check sum error

============13==============
P0601
Raw code: 0601
ECU: 10
Status: Confirmed
OBDII: Engine control module (ECM) - memory check sum error

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Welcome to TDP

All those loose "Unplugged" wires are indeed the issue.....

Does the engine still have the electronic injection pump ???? or did somebody change it to a manual injection pump.....

We need to figure out why all the wires are unplugged.

The ECM gets inputs from the injection pump (Electronic) and if the signals are not present the transmission will not shift......

Can you get a good picture of the top of the injection pump please.....

Thank you for the answer Robyn. I did my best to take a photo of the pump, but it is well hidden under the intake. Here is the link: https://imgur.com/a/eC3TOxT

Attachment 6422Attachment 6423Attachment 6424

BTW, I took also better photos of the connectors, there are 5 of them unplugged:

Attachment 6425Attachment 6426

Bingo

The injection pump is a DB2 mechanical pump.

I suspect that the engine was swapped and when the transmission issue came along the previous owner abandoned the project.

Getting a mechanical pump to work is possible....but it takes some fooling around.....

A stand alone transmission controller will make it work.

I am not sure of the cost or availability to you.

All the plugs are for the factory DS4 injection pump and will not work with the mechanical pump...

I know there are a few folks here that have done this swap......I am sure someone familiar with this set up will reply to the thread.....

I do know that a stand alone controller will work.

There has to be a throttle cable attached to the pedal.

The original set up had a "Fly by wire" electronic pedal "Electronic throttle"

Lets see who responds......

Try checking at usshift.com
Call these guys and tell them what you have (Mechanical injection pump in a later rig...need trans control)
My bet is they can help.

Thank you! That is interesting. Previous owner had it for 10 years and he drove thousands of kilometers with it. He states that he never had a problem with the engine. I think the engine was not swapped in last years, it looks like it sits in this car for whole 25 years. In fact, everything under the hood looks like it was not touched for a long time. You are also right with the throttle cable - I checked it out and I don't have electronic pedal, but again: it looks like a factory set up (photo). Would be nice to hear from someone who have it working with mechanical pump.

PS: Maybe the simplest way to get it working is to replace DB2 pump with electronic one?


Attachment 6427

OK I did some research about this. Now I know that replacing electronic pump with the mechanical one was quite a popular procedure back in time. I'm 99% sure that previous owner bought this car with pump/engine replaced. The car was imported to Poland from Canada and replacement procedure must have been done there because those cars are much more common in Canada.

So, as I understand, when the injection pump replacement is done, the car needs a stand alone transmission controller. Does this controller replace some of the existing transmission electronics, or it is an additional module? What about PCM codes that apply to the missing electronic pump, do you have to use e.g. resistors to fool the PCM? I think that my Tahoe has a stand alone transmission controller and there is something wrong with it or its wiring or some other elements of this system. That would clear up why previous owner told me, that local mechanics couldn't connect with transmission to diagnose it. PS: Is my transmission 4LE60 or 4LE80?

I will be REALLY grateful for any knowledge from you, the forum is my only way to get this car back on the road. :)

You need the high pressure injection lines and the injectors to go with the DS4 THEY ARE DIFFERENT....

The front of the engine has a different timing cover if it was not originally an electronic injected engine The crank position sensor is required....

Check the timing cover and see if it has the crank sensor.....If not....likely had an engine swap.

Today I looked at it closer. At first I checked transmission wiring - it has 2 main connectors, they were sitting tight in sockets and they were really rusty. Seems that they haven't been unplugged for years, I cleaned the corrosion before reconnecting them.

Then I checked out your suggestion:

Quote:

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Check the timing cover and see if it has the crank sensor.....If not....likely had an engine swap.

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Yes, there is a sensor (photo). I've checked its resistance and it seems to be fine. It is connected to a huge wiring harness at the back of the engine, near the firewall. Then I found that this big wire harness (it probably goes to PCM) is modified. Some of the cables from the unplugged harnesses (which I posted about yesterday) are cut off and soldered to cables from a big wire harness. I have re-soldered them because connections looked very old. Unfortunately it didn't help, engine light is still on and transmission doesn't shift gears. I think that injection pump has been replaced many years ago and everything was converted for a mechanical pump. Now I'm looking for some electric diagrams of the PCM to find out something more abot the cables that were modified.

Could you please tell me where the transmission controller should be located? And what transmission sits in my Tahoe, is it 4L60 or 4L80? I couldn't find any nameplate on it, just the number of converter cover: 15607697.

Transmission plugs:

Attachment 6428

Crank sensor:

Attachment 6429

Modified wire harness at the back of the engine (before re-soldering):

Attachment 6430

Quote:

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Check the timing cover and see if it has the crank sensor.....If not....likely had an engine swap.

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Yes, there is a sensor (photo). I've checked its resistance and it seems to be fine. It is connected to a huge wiring harness at the back of the engine, near the firewall. Then I found that this big wire harness (it probably goes to PCM) is modified. Some of the cables from the unplugged harnesses (which I posted about yesterday) are cut off and soldered to cables from a big wire harness. I have re-soldered them because connections looked very old, I attach a photo before a re-soldering. Unfortunately it didn't help, engine light is still on and transmission doesn't shift gears. I think that injection pump has been replaced many years ago and everything was converted for a mechanical pump. Now I'm looking for some electric diagrams of the PCM to find out something more abot the cables that were modified.

Could you please tell me where the transmission controller should be located? And what transmission sits in my Tahoe, is it 4L60 or 4L80? I couldn't find any nameplate on it, just the number of converter cover: 15607697.

With the large "mess" in the wiring I would recommend getting a "Stand alone" transmission controller module..(Available online)

These modules will have connections for the transmission and a throttle position sensor that will fasten to the injection pump..

The module assemblies come with good instructions for installation ....

IIRC for 1997, transmission control was integrated into the PCM. No TCM, for what should be a 4L80E. If it shifted before, since the MFI conversion, it has a controller, somewhere. You'll have to chase the harnesses to find it.