P0891
P0891 -TRANSMISSION RELAY ALWAYS ON
For a complete wiring diagram, refer to: Electrical Diagrams
When Monitored
After a reset (ignition key turned to the RUN position) and after a power down.
Set Condition
Relay output (Switched Battery) is higher than 3 volts when relay is not energized by controller. Fault Set Time: Less than 100 mSec.
Possible Causes
- TRANSMISSION CONTROL RELAY STUCK CLOSED
- (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT SHORT TO VOLTAGE
- (T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUITS SHORT TO VOLTAGE
- POWERTRAIN CONTROL MODULE
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Theory of Operation
The transmission relay is used to supply power to the solenoid pack when in normal operating mode, and to turn off power to produce transmission "limp-in" mode. The relay output (which supplies power to the solenoid pack) is fed back to the controller This is referred to as SWITCHED BATTERY After a controller reset (ignition key turned to the RUN position or after cranking engine), the controller verifies that the relay contacts are open by checking for no voltage on Switched battery line (i.e. relay output) before the relay is energized. Transmission locked in Limp-In. MIL on after 10 seconds of vehicle operation.
Diagnostic Test
1. CHECK TO SEE IF DTC P0891 IS CURRENT
With the scan tool, Check the STARTS SINCE SET counter for P0891.
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 6
2. TRANSMISSION CONTROL RELAY CONTACTS STUCK CLOSED
Turn the ignition off to the lock position.
Remove the Transmission Control Relay
NOTE: Check connectors - Clean/repair as necessary.
Measure the resistance between the Fused B+ circuit and the Transmission Control Relay Output Circuit of the Transmission Control Relay.
Is the resistance above 5.0 ohms?
Yes >> Go To 3
No >> Replace the Transmission Control Relay.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
3. (T16) TRANSMISSION RELAY OUTPUT CIRCUIT SHORT TO VOLTAGE
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.
Measure the voltage at the (T16) Transmission Control Relay Output circuit in the Transmission Control Relay connector.
Is the voltage above 0.5 volts?
Yes >> Repair the (T16) Transmission Control Relay Output circuit for a short to voltage.
Perform 42RLE TRANSMISSION VERIFICATION TEST -Ver 1. Verification Tests.
No >> Go To 4
4. (T15) TRANSMISSION CONTROL RELAY CONTROL CIRCUIT SHORT TO VOLTAGE
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.
NOTE: The Transmission Controller will power up the Transmission Control Relay Control circuit for approximately 3.0 seconds after initial ignition on. Wait at least 3.0 seconds before performing the following voltage check.
NOTE: A One-trip fault may set for P0888 Relay Always Off, disregard the DTC.
Measure the voltage at the (T15) Transmission Control Relay Control circuit after a 3.0 second wait period.
Is the voltage above 0.5 volts?
Yes >> Repair the (T15) Transmission Control Relay Control circuit for a short to voltage.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Go To 5
5. 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.
6. 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 DTC 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.