What Does P0887 Mean?
The TCM has detected a high voltage condition on the TCM power relay control circuit. The control circuit voltage is above the expected maximum, which may cause the relay to remain energized when it should be off or may indicate a short to a voltage source in the control wiring. This can prevent proper TCM power management.
Common Causes
35%
Short to battery voltage in relay control circuit wiring
25%
Relay control circuit shorted to another powered circuit
20%
TCM internal relay driver circuit stuck high
12%
Relay socket miswired or incorrect relay installed
8%
Charging system over-voltage affecting control circuit
Diagnostic Steps
1
Measure voltage on the relay control circuit with key on — if higher than expected, trace the source of the excess voltage.
2
Disconnect the TCM connector and re-measure the control circuit voltage — if still high, the short is in the wiring, not the TCM.
3
Inspect the wiring harness for chafing or damage where the relay control wire may contact other powered wires.
4
Verify the correct relay is installed — some relays have different pin configurations that can feed voltage back into the control circuit.
5
Check charging system voltage to ensure the alternator is not overcharging, which could elevate all circuit voltages.
Estimated Repair Cost
$50 - $700
Parts + labor, varies by vehicle and location
The TCM has detected a high voltage condition on the TCM power relay control circuit. The control circuit voltage is above the expected maximum, which may cause the relay to remain energized when it should be off or may indicate a short to a voltage source in the control wiring. This can prevent pro...
The most common cause of P0887 (TCM Power Relay Control Circuit High) is: Short to battery voltage in relay control circuit wiring
Typical repair costs for P0887 range from $50 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A continuously energized relay could keep the TCM powered when it should be off, potentially draining the battery overnight, or the high voltage could damage TCM electronics. Have the circuit inspected soon.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0887 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Control Module Power Supply
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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