P0888
P0888-TRANSMISSION RELAY ALWAYS OFF
For the Transmission circuit diagram Refer to Transmission Control Systems/Diagrams.
For a complete wiring diagram refer to diagrams.
^ When Monitored:
When the ignition is turned from "OFF" position to "RUN" position and/or the ignition is turned from "START" position to "RUN" position.
- Set Condition:
This DTC is set when less than 3.0 volts are present at the transmission control relay output circuits at the Powertrain Control Module when the PCM is energizing the relay.
Possible Causes
- (A104) FUSED B+ CIRCUIT OPEN
- (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN
- (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT SHORT TO GROUND
- (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT OPEN
- (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT SHORT TO GROUND
- (Z915) TRANSMISSION CONTROL RELAY GROUND CIRCUIT OPEN
- TRANSMISSION CONTROL RELAY STUCK OPEN
- POWERTRAIN CONTROL MODULE
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Theory of Operation
The transmission control relay is used to supply power to the solenoids and pressure switches when the transmission is in normal operating mode. The relay output is fed back to the TCM through pins 16, 17, and 36. It is referred to as "Transmission Control Relay Output". This circuit does not supply power to the TCM it is only a sense circuit. When the relay is off, no power is supplied to the solenoids and pressure switches, and the transmission is in "limp-in" or "default" mode. Note: Inadequate Transmission Control Relay Output voltage can also cause DTCs P0846, P0869, P0871, P0876 or P0988 to set. This does not indicate an internal transmission or solenoid/ TRS problem. Repairing the P0888 fault should also eliminate the related DTCs.
Diagnostic Test
1. CHECK TO SEE IF DTC P0888 IS CURRENT
With the scan tool, Check the STARTS SINCE SET counter for P0888.
NOTE: This counter only applies to the last DTC set.
Is the STARTS SINCE SET counter equal to 0?
Yes >>Go To 2
No >>Go To 9
2. (A104) FUSED B+ CIRCUIT OPEN
Turn the ignition off to the lock position. Remove the Transmission Control Relay.
NOTE: Check connectors - Clean/repair as necessary.
Ignition on, engine not running.
Using a 12-volt test light connected to ground, check the (A104) Fused B+ circuit in the Transmission Control Relay connector.
NOTE: The test light must illuminate brightly. Compare the brightness to that of a direct connection to the battery.
Does the test light illuminate brightly?
Yes >>Go To 3
No >>Repair the (A104) Fused B+ circuit for an open. If the fuse is open make sure to check for a short to ground.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
3. (Z915) TRANSMISSION CONTROL RELAY GROUND CIRCUIT OPEN
Turn the ignition off to the lock position. Using a 12-volt test light connected to 12-volts, check the (Z915) Transmission Control Relay Ground circuit in the Transmission Control Relay connector.
Does the test light illuminate brightly?
Yes >>Repair the (Z915) Transmission Control Relay Ground circuit for an open.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
No >>Go To 4
4. TRANSMISSION CONTROL RELAY
Install a substitute relay in place of the Transmission Control Relay.
Start the vehicle.
With the scan tool, check transmission DTCs.
Did the DTC P0888 reset?
Yes >>Replace the Transmission Control Relay.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
No >>Go To 5
5. (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN
Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector and connect Miller tool #88 1 5.
Disconnect the Transmission Solenoid/TRS Assembly harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller tool #8815 to perform diagnosis.
Connect a jumper wire between the (A104) Fused B+ circuit and the Transmission Control Relay Output circuit in the Transmission Control Relay connector.
Ignition on, engine not running.
Using a 12-volt test light connected to ground, check all four (T16) Transmission Control Relay Output circuits in the PCM C4 harness connector and Transmission Solenoid/TRS Assembly harness connector.
Does the test light illuminate brightly on all four (T16) Transmission Control Relay Output circuits?
Yes >>Go To 6
No >>Repair the (T16) Transmission Control Relay Output circuit(s) for an open or high resistance.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
6. (T16) TRANSMISSION RELAY OUTPUT CIRCUIT SHORT TO GROUND
Turn the ignition off to the lock position.
Measure the resistance between ground and the (T16) Transmission Control Relay Output circuit.
Is the resistance below 5.0 ohms?
Yes >>Repair the (T16) Transmission Control Relay Output circuit for a short to ground.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
No >>Go To 7
7. (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT SHORT TO GROUND
Measure the resistance between ground and the (T15) Transmission Control Relay Control circuit. I
Is the resistance below 5.0 ohms?
Yes >>Repair the (T15) Transmission Control Relay Control circuit for a short to ground.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
No >>Go To 8
8. (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT OPEN
Measure the resistance of the (T15) Transmission Control Relay Control circuit between the Transmission Control Relay connector and the appropriate terminal of Miller tool #8815.
Is the resistance above 5.0 ohms?
Yes >>Repair the (T15) Transmission Control Relay Control circuit for an open.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
No >>Using the schematics as a guide, check the Powertrain Control Module (PCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the PCM per the Service Information. With the scan tool, perform QUICK LEARN.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
9. INTERMITTENT WIRING AND CONNECTORS
The conditions necessary to set this DTC are not present at this time.
Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
Wiggle the wires while checking for shorted and open circuits.
With the scan tool, check the EATX DTC EVENT DATA to help identify the conditions in which the DTC was set.
Where there any problems found?
Yes >>Repair as necessary.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
No >>Test Complete.