P0888
P0888-TRANSMISSION RELAY ALWAYS OFF
For a complete wiring diagram, refer to: Electrical Diagrams
When Monitored
Continuously
Set Condition
This DTC is set when less than 3 volts are present at the Transmission Control Relay output circuits at the Powertrain Control Module when the PCM is energizing the relay. Note: Due to the integration of the Powertrain and Transmission Control Modules, the transmission part of the PCM has its own specific power and ground circuits.
Possible Causes
- (Internal) FUSED B+ CIRCUIT OPEN
- (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN
- (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT OPEN
- (Z901) TRANSMISSION CONTROL RELAY GROUND CIRCUIT OPEN
- (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT SHORT TO GROUND
- (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT SHORT TO GROUND
- TRANSMISSION CONTROL RELAY
- TRANSMISSION SOLENOID/PRESSURE SWITCH ASSEMBLY
- 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 solenoid pack when the transmission is in normal operating mode. When the relay is off, no power is supplied to the solenoid pack and the transmission is in Limp-in mode. The relay output is fed back to the PCM. It is referred to as the Trans Relay Output circuit or switched battery. After a controller reset (ignition key turned to the run position or after cranking engine), the controller energizes the relay. Prior to this, the PCM verifies that the contacts are open by checking for no voltage at the transmission control relay outputs (switched battery) terminals. After the relay is energized, the PCM monitors the terminals to verify that the voltage is greater than 3 volts. The MIL illuminates and the transmission will be placed in Limp-in.
Diagnostic Test
1. CHECK TO SEE IF DTC P0888 IS CURRENT
With the scan tool, Check the STARTS SINCE SET counter for P088.
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 12
2. CHECK THE (INTERNAL) FUSED B+ CIRCUIT
Turn the ignition off to the lock position.
Remove the Transmission Control Relay
NOTE: Check connectors - Clean/repair as necessary.
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 3
No >> Go To 9
3. (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN
Turn the ignition off to the lock position.
Remove the Transmission Control Relay
NOTE: Check connectors - Clean/repair as necessary.
Connect a jumper wire between the (Internal) Fused B+ circuit and the (T16) Transmission Control Relay Output circuits. Ignition on, engine not running. With the scan tool in Transmission Sensors, read the Switched Battery voltage.
Does the Switched Battery voltage read battery voltage?
Yes >> Go To 4
No >> Repair the (T16) Transmission Control Relay Output circuits for an open or high resistance. Note: There are multiple Transmission Control Relay Output circuits.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
4. TRANSMISSION CONTROL RELAY
Turn the ignition off to the lock position.
Install a substitute Relay in place of the Transmission Control Relay.
Ignition on, engine not running.
With the scan tool in Transmission Sensors, read the Switched Battery voltage.
Does the Switched Battery voltage read battery voltage?
Yes >> Replace the Transmission Control Relay.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Go To 5
5. (Z901) TRANSMISSION CONTROL RELAY GROUND CIRCUIT OPEN
Turn the ignition off to the lock position.
Remove the Transmission Control Relay
NOTE: Check connectors - Clean/repair as necessary.
Using a 12-volt test light connected to 12-volts, check the (Z901) Transmission Control Relay Ground circuit.
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 6
No >> Repair the (Z901) Transmission Control Relay Ground circuit for an open.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
6. (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT OPEN
Turn the ignition off to the lock position.
Remove the Transmission Control Relay.
Disconnect the PCM C4 harness connector.
NOTE: Check connectors - Clean/repair as necessary.
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.
Measure the resistance of the (T15) Transmission Control Relay Control circuit between the Transmission Control Relay connector and the appropriate terminal of special tool #8815.
Is the resistance above 5.0 ohms?
Yes >> Repair the (T15) Transmission Control Relay Control circuit for an open.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Go To 7
7. (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT SHORT TO GROUND
Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector.
Remove the Transmission Control Relay
NOTE: Check connectors - Clean/repair as necessary.
Measure the resistance between ground and the (T15) Transmission Control Relay Control circuit.
Is the resistance below 5.0 ohms?
Yes >> Repair the (T15) Transmission Control Relay Control circuit for a short to ground.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Go To 8
8. POWERTRAIN CONTROL MODULE
Using the schematics as a guide, inspect the wiring and connectors. Repair as necessary Pay particular attention to all power and ground circuits.
If there are no possible causes remaining, view repair.
Repair
Replace the Powertrain Control Module per the Service Information. With the scan tool PERFORM QUICK LEARN, then program Pinion Factor in the Front Control Module.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
9. OPEN FUSE
Turn the ignition off to the lock position.
Remove the Transmission Control Relay
Disconnect the PCM C4 harness connectors.
NOTE: Check connectors - Clean/repair as necessary.
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.
Measure the resistance between ground and the (T16) Transmission 86 85 Control Relay Output circuit.
Is the resistance below 5.0 ohms?
Yes >> Go To 10 TRANSMISSION CONTROL
No >> Repair the Fused B+ circuit for an open. (RLE) Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
10. (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT SHORT TO GROUND
Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector.
Disconnect the Transmission Solenoid/Pressure Switch harness connector.
Remove the Transmission Control Relay
NOTE: Check connectors - Clean/repair as necessary.
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 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Go To 11
11. TRANSMISSION SOLENOID/PRESSURE SWITCH ASSEMBLY
Using the schematics as a guide, inspect the wiring and connectors.
Repair as necessary Pay particular attention to all power and ground circuits.
If there are no possible causes remaining, view repair.
Repair
Replace the Transmission Solenoid/Pressure Switch Assembly per the Service Information.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
12. INTERMITTENT WIRING AND CONNECTORS
The conditions necessary to set the DTC are not present at this time.
Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
Wiggle the wiring and connectors while checking for shorted and open circuits.
With the scan tool, check the EATX EVENT DATA to help identify the conditions in which the DTC was set.
Were there any problems found?
Yes >> Repair as necessary.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Test Complete.