DTC P1600 Serial Communication between PCM and TCM. Geo Tracker

For 1990-2009 cars only

Makes 🢒 Geo 🢒 1996 🢒 Tracker - 4WD 🢒 DTC 🢒 DTC P1600 Serial Communication between PCM and TCM

Schematic Reference: Engine Controls Schematics

Circuit Description

The transmission control module (TCM) uses a serial data circuit in order to communicate with the engine control module (ECM). The serial data circuit between the ECM and the TCM is noramlly 5 volts.

Conditions for Setting the DTC

•	The engine is running.

•	No communication from the TCM has occurred for a specified amount of time.

Action Taken When the DTC Sets

•	The ECM illuminates the malfunction indicator lamp (MIL).

•	The ECM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

Diagnostic Aids

Check for any of the following conditions:

•	Backed out terminals.

•	Improper mating of terminals.

•	Broken electrical connector locks.

•	Improperly formed or damaged terminals.

•	Faulty terminal to wire connections.

•	Physical damage to the wiring harness.

•	A broken wire inside the insulation.

•	Corrosion of electrical connections, splices, or terminals.

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

This step checks for a communication signal to the ECM. The voltage should be toggling high and low between 0-5 volts. There is no communication if the voltage remains at zero or at 5 volts.

This step checks for a good ground and positive voltage connections to the TCM. The TCM cannot operate correctly without these circuits.

Step	Action	Value(s)	Yes	No
1	Did you Perform the Powertrain On-Board Diagnostic (OBD) System Check?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Turn ON the ignition, leaving the engine OFF. Backprobe the TCM serial data circuit at the ECM connector with a DMM connected to ground. Is the voltage measured toggling within the specified value?	0-5 V	Go to Step 3	Go to Step 4
3	Perform the scan tool clear DTC information function. Operate the vehicle within the Freeze Frame conditions as noted. Did a DTC P1600 set?	B+	Go to Step 4	Go to Diagnostic Aids
4	Turn OFF the ignition. Disconnect the TCM electrical connector. Turn ON the ignition, leaving the engine OFF. Backprobe the TCM serial data circuit at the TCM connector with a DMM connected to ground. Is the voltage at the specified value?	5 V	Go to Step 6	Go to Step 5
5	Check for an open or a short to ground in the serial data circuit between the ECM and the TCM. Repair as necessary. Was a repair necessary?	--	Go to Step 9	Go to Step 8
6	Check for good power and ground connections to the TCM. Refer to Automatic Transmission Controls Schematics in Automatic Transmission--4 Speed. Repair as necessary. Was a repair necessary?	--	Go to Step 9	Go to Step 7
7	Replace the TCM. Is the action complete?	--	Go to Step 9	--
8	Replace the ECM. Refer to Engine Control Module Replacement. Is the action complete?	--	Go to Step 9	--
9	Perform the scan tool DTC Information function and road test the vehicle within the conditions that set the DTC. Check for DTCs. Review the scan tool data. If no DTCs are set, the repair is complete. Are any DTCs displayed on the scan tool?	--	Go to the Applicable DTC Table	System OK