Circuit Description
The Shift Solenoids, the Band Apply Solenoid, and the TCC Solenoid are supplied power via the Transmission Power Relay (internal to the TCM) on TCM pin 54. The Pressure Control Solenoid is also supplied power via the Transmission Power Relay (internal to the TCM) but on TCM pin 40. TCM pins 54 and 40 are connected within the TCM. The TCM controls the solenoids by grounding the appropriate control circuit via internal solid state devices called drivers. The driver circuits have their own fault detection abilities that identify problems with individual solenoids/circuits. The TCM also has fault detection circuitry for the power supply circuit that powers all of the solenoids in the transmission. If the TCM detects a problem with this circuit, DTC P1600 will set, and the TCM will shut off the Transmission Power Relay. Any time a TCM DTC is set that requires the transmission to operate in Default Mode, the TCM turns off the power relay, effectively disabling all of the transmission solenoids. Any time the Default Mode is in effect, the transmission line pressure is at maximum, and the transmission starts in 4th gear.
Conditions For Running The DTC
Tests continuously
Conditions for Setting the DTC
A short to ground, open circuit, or short to battery voltage detected on the control circuit.
Action Taken When the DTC Sets
| • | The TCM illuminates the Service Transmission Lamp (STL) and sends a MIL Request to the ECM on the second consecutive drive trip that the diagnostic runs and fails. The ECM then illuminates the MIL. |
| • | The ECM records the operating conditions in the Freeze Frame at the time of the MIL Request from the TCM. |
| • | The transmission operates in the Default Mode. |
Conditions for Clearing the MIL/DTC
| • | The TCM turns off the STL as soon as the fault is no longer present. |
| • | The ECM turns off the MIL after three consecutive drive trips during which the TCM sends no MIL Request. |
| • | A History DTC clears after forty consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission related diagnostic. |
| • | The scan tool clears the MIL/DTC. |
Diagnostic Aids
Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the TCM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.
Check for the following conditions:
| • | Poor connections at the TCM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure. |
| • | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any related connectors and any wiring harnesses. A change in the display may help to locate the fault. |
Test Description
The number(s) below refer to the step numbers on the diagnostic table.
-
Allows the TCM to determine if the fault is present now.
-
This test determines if the Transmission Power Relay output circuit is open between the TCM and the splice. For this DTC to set from an open circuit, the open would have to be between the TCM and the splice. An open in either of the circuits after the splice would set DTCs for the affected solenoids only.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Is DTC P1600 set? | -- | No trouble found Refer to Diagnostic Aids | ||
3 |
Does the test light illuminate? | -- | ||
4 | With the test light connected to B+, probe the Transmission Power Relay output circuit in the TCM harness connector. Does the test light illuminate? | -- | ||
5 |
Does the test light illuminate? | -- | ||
6 |
Does the test light illuminate? | -- | ||
Use a DVM J 39200 in order to check the harness for continuity of the Transmission Power Relay output circuit from the TCM harness connector to either the Main Case or Adapter Case harness connector. Is continuity indicated? | -- | |||
8 | Repair the Power Relay output circuit shorted to B+. Is the action complete? | -- | -- | |
9 | Repair the Power Relay output circuit shorted to ground. Is the action complete? | -- | -- | |
10 | Repair the open/high resistance Power Relay output circuit. Is the action complete? | -- | -- | |
11 | Repair the Transmission Power Relay output circuit shorted to ground in the Adapter Case. Is the action complete? | -- | -- | |
12 | Repair the Transmission Power Relay output circuit shorted to ground in the Main Case. Is the action complete? | -- | -- | |
13 | Check the TCM harness connector for a poor connection or poor terminal tension. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure. Was a problem found and corrected? | -- | ||
14 | Replace the TCM. Refer to Automatic Transmission, On Vehicle Service, TCM. Is the action complete? | -- | -- | |
15 |
Is DTC P1600 set? | -- | ||
16 | Were there any additional DTCs noted during the Powertrain or Transmission OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | |
17 | Does the Transmission now function properly? | -- | System OK | Go to Functional Test |
