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No Communication With TCM

kdailey4315

NAXJA Forum User
Location
Pacifica, CA
My code reader can not communicate with my TCM. I get an error that says Can't communicate with the TCM make sure ignition is on etc. I was able to pull codes from the TCM before I cleaned my NSS. Did I screw something up?

98 Limited AW4 D30/35
 
My code reader can not communicate with my TCM. I get an error that says Can't communicate with the TCM make sure ignition is on etc. I was able to pull codes from the TCM before I cleaned my NSS. Did I screw something up?

98 Limited AW4 D30/35

If you disconnected the NSS (Transmission Range Sensor) connector, next to the transmission dipstick, to service the NSS, there is a possibility you disturbed a pin or two in that connector. You may want to disconnect and inspect the pins/cavities.

Does your NSS function properly? Does your Transmission shift properly?

Why did you clean your NSS?

"I was able to pull codes from the TCM before I cleaned my NSS". What codes were you pulling?
 
^^Good questions... Anything other than P0700 and P0705 needs to be reported. For the PCM to say it can't communicate with the TCM implies, well, a loss of comunication (sorry, but really...). The CCD Bus has lost touch with the TCM.

We do need all of the codes. Pre and Post NSS clean.
 
For clarification, below is a pic of your datalink connector pin-out and a CCD bus schematic.

Note that pin 7 of the DLC is the Serial Communications Interface with the TCM. Pin 7 SCI is the pin that provides a scanner with read out information (codes, etc.) If the SCI wire between the TCM and the DLC is open the scanner will notify you there is no communication with the TCM. Note also that the CCD communication bus includes the TCM and PCM. This link is required for the TCM to function. If this link is broken your PCM will think the TCM doesn't exist and you will have shifting problems. An open SCI link will only tell you there is no communication with a module. Note that the SCI wiring is not shown on the CCD bus schematic, but is explained in the DLC table.

You can test the CCD bus using a digital voltmeter but you can't test the SCI transmit signals. If you want to test the CCD let us know. If you want to ring out the wire between the TCM and pin 7 of the DLC let us know.

XJCCDDLC.jpg
 
If you disconnected the NSS (Transmission Range Sensor) connector, next to the transmission dipstick, to service the NSS, there is a possibility you disturbed a pin or two in that connector. You may want to disconnect and inspect the pins/cavities.

I will inspect the pins today

Does your NSS function properly? Does your Transmission shift properly?
Now it is functioning properly. It seems like my transmission shifts into OD early, around 45MPH. Then the RPMs drop to about 150 and it feels like my Jeep luggs.

Why did you clean your NSS?
No reverse lights and P700/P705 code

"I was able to pull codes from the TCM before I cleaned my NSS". What codes were you pulling?
P700/P705 and shift solenoid code. Either P740 or P45 I can't remember.



^^Good questions... Anything other than P0700 and P0705 needs to be reported. For the PCM to say it can't communicate with the TCM implies, well, a loss of comunication (sorry, but really...). The CCD Bus has lost touch with the TCM.

We do need all of the codes. Pre and Post NSS clean.

Pre NSS clean Those 3 I mentioned above. Post NSS clean 1685, Low charging system but no CEL. Can't pull any transmission specific codes.
 
Do you have a Security Key Immobilizer system in your Jeep? P1685 is SKIM Invalid Key - The engine controller (PCM) has received an invalid key from the SKIM. See schematic above. P1685 will not trigger a CEL.
 
"P1682 Charging System Voltage Too Low" This is what my book says... Verify the charge rate with a meter. Needs to be above 14VDc.

Pacifica... Pacific Ocean due west and the Coastal Range due east. If it snowed on the top of the range it would be a perfect place to live... I like the area.



 
"P1682 Charging System Voltage Too Low" This is what my book says... Verify the charge rate with a meter. Needs to be above 14VDc.

Pacifica... Pacific Ocean due west and the Coastal Range due east. If it snowed on the top of the range it would be a perfect place to live... I like the area.




I checked the voltage. 12.7V with the car off. 14.1 volts with the car running.

I love Pacifica. I'm 3 blocks from the Ocean so I can't complain. It would be awesome if it snowed here though.
 
For clarification, below is a pic of your datalink connector pin-out and a CCD bus schematic.

Note that pin 7 of the DLC is the Serial Communications Interface with the TCM. Pin 7 SCI is the pin that provides a scanner with read out information (codes, etc.) If the SCI wire between the TCM and the DLC is open the scanner will notify you there is no communication with the TCM. Note also that the CCD communication bus includes the TCM and PCM. This link is required for the TCM to function. If this link is broken your PCM will think the TCM doesn't exist and you will have shifting problems. An open SCI link will only tell you there is no communication with a module. Note that the SCI wiring is not shown on the CCD bus schematic, but is explained in the DLC table.

You can test the CCD bus using a digital voltmeter but you can't test the SCI transmit signals. If you want to test the CCD let us know. If you want to ring out the wire between the TCM and pin 7 of the DLC let us know.

How would I test that? Is it spelled out for me in the FSM? I have the regular FSM and the transmission one.
 
First, has code P1682 been cleared?

~~~~~~~~~

Checking TCM on CCD Bus:

Use a digital volt/ohmmeter....

Disconnect and isolate negative battery cable from battery,

Refer to the schematic above,

Detach connector from the TCM,

Refer to the TCM pin out drawing below (view looking at the detached TCM connector),

TCMXJConnectorPinOut.jpg


Using your digital ohmmeter, measure for continuity (near 0 resistance) between pin 6 of the TCM connector and pin 11 of the Data Link Connector (DLC), Check for resistance between pin 7 of the TCM connector and pin 3 of the DLC. Any high resistance or open indicates the TCM may not be connected to the CCD Bus.

The same process can be used to check the SCI Transmit TCM wire. Measure for continuity beteen pin 14 of the TCM connector and pin 7 of the DLC. An open or high resistance reading may indicate the TCM SCI signal is not connected to the DLC (scanner).

While you're here, using your digital ohmmeter, measure for continuity beteen pin 24 of the TCM connector (TCM ground to ground point G101 on engine) and a good chassis ground (gas pedal pivot bracket mount bolt is good).

~~~~~~

Attach TCM connector,

Attach negative battery connector.

~~~~~~

Using your digital voltmeter....

Turn ignition switch to Run (engine off),

Touch positive probe of voltmeter to pin 3 of the DLC and negative probe of the voltmeter to pin 4 of the DLC. You should read about 4.5 volts. Touch the positive probe to pin 11 of the DLC and the negative probe to pin 4 of the DLC. You should read about 4.5 volts.

Voltage readings significantly out of range of the 4.5 volts may indicate a module on the CCD bus is corrupting the bus.
 
Thanks for the info. The P1682 code has not been cleared. Yesterday I tested the voltage and got 12.7V engine off and 14.1V engine running. Isn't that normal?
 
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