What Does P0891 Mean?
The PCM or TCM has detected a higher-than-expected voltage on the transmission control module power relay sense circuit. This typically indicates the sense circuit is shorted to a voltage source or the relay is stuck in the energized position. The TCM uses this circuit to confirm the power relay is operating correctly, and an abnormally high signal disrupts that verification.
Safety Warning
An always-on power relay or high sense voltage can prevent the TCM from properly managing power states, potentially causing erratic transmission behavior or failure to enter sleep mode, which can drain the battery and cause unexpected shifts.
Common Causes
30%
TCM power relay stuck closed or welded contacts
25%
Short to battery voltage in the TCM power relay sense circuit wiring
20%
Corroded or damaged connector causing voltage feedback on the sense circuit
15%
Faulty TCM internal circuitry reading incorrect sense voltage
10%
Incorrect relay installed or miswired after previous repair
Diagnostic Steps
1
Locate the TCM power relay and remove it; check if the sense circuit voltage drops to zero with the relay removed. If voltage remains, a short to power exists in the wiring.
2
Test the TCM power relay for stuck or welded contacts using an ohmmeter; the contacts should be open when the relay is not energized.
3
Inspect the wiring harness from the relay to the TCM for chafing against hot or sharp surfaces that could create a short to battery voltage.
4
Verify the correct relay part number is installed, especially if a recent relay replacement was performed.
5
If the relay and wiring check out, monitor the sense circuit voltage at the TCM connector with a scope to identify intermittent spikes; a faulty TCM may be suspected.
Estimated Repair Cost
$150 - $700
Parts + labor, varies by vehicle and location
The PCM or TCM has detected a higher-than-expected voltage on the transmission control module power relay sense circuit. This typically indicates the sense circuit is shorted to a voltage source or the relay is stuck in the energized position. The TCM uses this circuit to confirm the power relay is ...
The most common cause of P0891 (TCM Power Relay Sense Circuit High) is: TCM power relay stuck closed or welded contacts
Typical repair costs for P0891 range from $150 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An always-on power relay or high sense voltage can prevent the TCM from properly managing power states, potentially causing erratic transmission behavior or failure to enter sleep mode, which can drain the battery and cause unexpected shifts.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0891 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission
Difficulty
Type
Generic (SAE)
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