P0888-TRANSMISSION RELAY ALWAYS OFF

For a complete wiring diagram Refer to Section 8W.

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.

When Monitored:
Continuously
Set Condition:
This DTC is set when the Transmission Control Relay output circuit voltage at the Powertrain Control Module is less than 3 volts 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

(A104) FUSED B+ CIRCUIT OPEN

(T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN

(T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT OPEN

(Z915) TRANSMISSION CONTROL RELAY GROUND CIRCUIT OPEN

(T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT SHORT TO GROUND

(A104) FUSED B+ 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 42RLE Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)

Diagnostic Test

1. CHECK TO SEE IF DTC P0888 IS CURRENT

With the scan tool, view DTCs.

Is the status Active for this DTC or is the STARTS SINCE SET counter equal to 0?

Yes

Go To 2

Go To 12

2. CHECK THE (A104) FUSED B+ CIRCUIT FOR VOLTAGE

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 (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

Go To 9

3. (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN

Connect a jumper wire between the (A104) Fused B+ circuit and the (T16) Transmission Control Relay Output circuits at the Transmission Control Relay connector.
Ignition on, engine not running.
With the scan tool, read the Transmission Switched Battery voltage.

Is the Switched Battery voltage equal to battery voltage?

Yes

Go To 4

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. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)

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, read the Transmission Switched Battery voltage.

Is the Switched Battery voltage equal to battery voltage?

Yes

Replace the Transmission Control Relay.

Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)

Go To 5

5. (Z915) TRANSMISSION CONTROL RELAY GROUND CIRCUIT OPEN

Using a 12-volt test light connected to 12-volts, check the (Z915) 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

Repair the (Z915) Transmission Control Relay Ground circuit for an open.
Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)

6. (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT OPEN

Turn the ignition off to the lock position.
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.