P0888
P0888-TRANSMISSION RELAY ALWAYS OFF
For a complete wiring diagram Consult Diagrams/Electrical.
Theory of Operation
The Transmission Control Output circuit is used to supply power to the Transmission Solenoid/TRS Assembly and to the PCM when in normal operating mode. The purpose of the Transmission Output circuit is to allow the Transmission Control System to turn off the power to the Transmission Solenoid/TRS Assembly in event that the transmission should need to be placed into "limp-in" mode due to a DTC.
After a PCM reset, (ignition switch turned to the run position, or after cranking the engine) the Transmission Control System verifies that the Transmission Output circuit is open by checking for voltage on the Transmission Output circuits before the Transmission Control System request for the circuit to be powered up. The request is sent by a direct circuit control from the PCM to the TIPM. If the Transmission Control System detects less than 3.0 volts when the output is commanded on, the DTC will set. Note: Inadequate Transmission Control Output voltage can also cause DTCs P0846, or P0871, to set. This does not indicate an internal transmission or solenoid/TRS problem. Repairing the P0882 fault should also eliminate the related DTCs.
- 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 there is less than 3.0 volts present at the transmission control output circuits located in the Powertrain Control Module (PCM) when the Transmission Control System request the power up of those circuits. Note: Due to the integration of the Transmission Control Module and the Powertrain Control Module, both systems have their own power and ground circuits.
Always perform the 62TE Pre-Diagnostic Troubleshooting procedure before proceeding.Testing and Inspection
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 10
2. TRANSMISSION CONTROL RELAY
Turn the ignition off to the lock position.
Remove the Transmission Control Relay.
NOTE: Check connectors - Clean/repair as necessary.
Install a substitute Relay in place of the Transmission Control Relay.
Ignition on, engine not running.
With the scan tool, monitor the Switched Battery voltage in the next step.
NOTE: The switched battery voltage should remain steady and around 12-volts
Does the Switched Battery voltage remain a steady voltage (12-volts) and the DTC not reset?
Yes
- Replace the Transmission Control Relay.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
No
- Go To 3
3. CHECK THE (INTERNAL) FUSED B(+) CIRCUIT
Turn the ignition off to the lock position.
Remove the Transmission Control Relay.
Ignition on, engine not running.
Using a 12-volt test light connected to ground, check the (Internal) 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 4
No
- Go To 8
4. (T16) TRANSMISSION CONTROL OUTPUT CIRCUIT OPEN
Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector and install Miller tool #8815.
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 Special Tool #8815 to perform diagnosis.
Connect a fused jumper wire between the (Internal) Fused B(+) circuit and the (T16) Transmission Control Output circuit in the Transmission Control Relay connector.
Ignition on, engine not running.
CAUTION: Using a low impedance test light can damage computer circuitry. Make sure to double check the circuit identification before testing.
Using a low impedance test light connected to ground, check the (T16) Transmission Control Output circuits in the Miller tool #8815.
Does the test light illuminate brightly?
Yes
- Go To 5
No
- Repair the (T16) Transmission Control Output circuits for an open or high resistance. Note: There are multiple Transmission Control Output circuits and usually derive from a common splice. Make sure to inspect the splice for corrosion or water intrusion and repair as necessary.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
5. (Z115) GROUND CIRCUIT OPEN
Using a 12-volt test light connected to 12-volts, check the (Z115) Ground circuit in the Transmission Control Relay connector.
Does the test light illuminate brightly?
Yes
- Go To 6
No
- Repair the (Z115) Ground circuit for an open.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
6. (T15) TRANSMISSION CONTROL CIRCUIT OPEN
Turn the ignition off to the lock position.
Measure the resistance of the (T15) Transmission 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 circuit for an open.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
No
- Go To 7
7. (T15) TRANSMISSION CONTROL CIRCUIT SHORT TO GROUND
Measure the resistance between ground and the (T15) Transmission Control circuit.
Is the resistance below 5.0 ohms?
Yes
- Repair the (T15) Transmission Control circuit for a short to ground.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
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. With the scan tool PERFORM QUICK LEARN, then program Pinion Factor in the Front Control Module.Powertrain Control Module - Removal
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
8. OPEN FUSE
Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector.
Measure the resistance between ground and the (T16) Transmission Control Output circuit.
Is the resistance below 5.0 ohms?
Yes
- Go To 9
No
- Repair the Fused B(+) circuit for an open.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
9. (T16) TRANSMISSION CONTROL OUTPUT CIRCUIT SHORT TO GROUND
Disconnect the Transmission Solenoid/Pressure Switch harness connector.
Disconnect the Line Pressure Sensor/Variable Force Solenoid harness connector.
Measure the resistance between ground and the (T16) Transmission Control Output circuit.
Is the resistance below 5.0 ohms?
Yes
- Repair the (T16) Transmission Control Output circuit for a short to ground.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
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. Check for Service Information Tune-ups or Service Bulletins for any possible causes that may apply. If no problems are found, replace and program the PCM. With the scan tool, perform QUICK LEARN.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
10. CHECK THE 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 DTC EVENT DATA to help identify the conditions in which the DTC was set.
Where there any problems found?
Yes
- Repair as necessary.
- PERFORM 62TE VERIFICATION TEST Transmission Verification Test
No
- Test Complete.