P0891 — TCM Power Relay Sense Circuit High #

Note: The label for DTC P0891 may vary depending on the vehicle manufacturer (OEM). Always refer to your vehicle’s service manual for the exact wording.

• TCM Power Relay Sense Circuit High (General, most OEMs)
• Transmission Control Module Power Relay Sense Circuit High (Ford, GM, Chrysler)
• TCM Control Relay Feedback Circuit High (Honda/Acura)

Summary of DTC P0891 #

Diagnostic Trouble Code P0891 indicates that the Transmission Control Module (TCM) has detected a high voltage condition in the power relay sense circuit. The TCM is responsible for monitoring and controlling your vehicle’s automatic transmission. The power relay sense circuit is a feedback circuit used by the TCM to confirm that the transmission power relay is functioning and providing power as expected. When the circuit reads higher voltage than specified, it may point to issues with the relay itself, its control wiring, or sometimes the TCM. If left unresolved, this could affect shifting quality or even transmission operation.

Common Symptoms for Code P0891 #

P0891 can manifest with a range of symptoms, depending on the vehicle and the severity of the fault. In some cases, the driver may barely notice an issue; in others, the vehicle may enter limp mode (a safety feature that limits gear selection and speed to protect the transmission). Be alert to the following signs:

• Check Engine Light illuminated
• Transmission warning light on some models
• Harsh or erratic shifting
• Transmission stuck in a single gear (often 2nd or 3rd)
• Failure to shift at all
• Reduced power or acceleration
• Intermittent or no communication with the TCM during scan tool diagnostics

Probable Causes for Code P0891 #

Most P0891 issues stem from electrical faults rather than mechanical problems inside the transmission. The most frequent causes, in order of likelihood, are:

1. Faulty transmission power relay (sticking or internal short)
2. Damaged or corroded relay control wiring (open circuits, short to power, or high resistance)
3. Poor electrical connections (at relay socket, TCM connector, or fuse box)
4. Blown fuse in the transmission relay or main circuit
5. Faulty Transmission Control Module (TCM)

Step-by-Step Diagnosis for P0891 #

A systematic approach will help you pinpoint the root cause of P0891. Always follow safety guidelines and disconnect the battery when working with electrical systems.

1. Scan for additional codes: Note any other codes, especially TCM or power supply related (e.g., P0880, P0882).
2. Check battery voltage: Confirm battery is fully charged and charging system is healthy.
3. Inspect transmission power relay: Locate the relay (refer to OEM diagram), check for damage, corrosion, or loose mounting.
4. Test relay operation: Swap with a known-good relay if possible, or bench-test using a multimeter to confirm switching function.
5. Inspect and test wiring: Check relay control and sense circuit wiring for continuity, resistance, and shorts to power or ground.
6. Check TCM connector and grounds: Look for bent pins, corrosion, or loose connections at the TCM and chassis ground points.
7. Verify fuse integrity: Inspect all fuses related to the transmission and relay circuits.
8. Test TCM output: If all else checks out, verify TCM is sending correct signals to the relay (requires advanced diagnostic tools).

Possible Repairs for P0891 #

Once you’ve identified the cause, the appropriate repair depends on what you found. Most solutions involve repair or replacement of basic electrical components:

• Replace the transmission power relay if it fails test or shows signs of wear/corrosion.
• Repair or replace damaged wiring in the relay control or sense circuit.
• Clean or tighten electrical connectors at the relay, TCM, and fuse box.
• Replace any blown fuses and investigate underlying causes for fuse failure.
• Replace the TCM if it is confirmed to be faulty (rare, but possible).

Can You Drive with Code P0891? #

Limited: While some vehicles may drive normally with P0891, many will experience limp mode or shifting issues. Prolonged driving with this code can lead to further transmission or electrical damage. If the vehicle is stuck in one gear or shifts harshly, avoid driving and address the issue promptly. Even if symptoms are mild, have the problem diagnosed as soon as possible to prevent future complications.

Vehicles Most Commonly Affected by P0891 #

P0891 is seen across a range of makes and models, but is most frequently reported on vehicles with electronically controlled automatic transmissions. Notably:

• Chrysler/Dodge/Jeep (2000s–2010s, especially minivans and trucks)
• Ford (Explorer, F-150, Edge, Escape, 2005–2015)
• GM/Chevrolet (Silverado, Malibu, Equinox, 2007–2016)
• Honda/Acura (certain 2010s models)
• Hyundai/Kia (Sonata, Santa Fe, 2011–2016)

Always verify with your vehicle’s specific wiring diagram and TSBs (Technical Service Bulletins) for known issues related to P0891.

Common Mistakes & Best Practices for P0891 #

Misdiagnosis of P0891 often results from overlooking simple electrical problems or skipping diagnostic steps. To avoid wasted time and repeated failures, keep these tips in mind:

• Don’t replace the TCM first: Most P0891 codes are caused by relay or wiring faults, not the module itself.
• Always check fuses and relays physically, not just visually—use a multimeter.
• Document wiring repairs: Use OEM wiring diagrams and avoid splicing or bypassing circuits without proper connectors and sealing.
• Clear codes and retest after each repair to ensure the fault is resolved, not masked.

Quick FAQ for Code P0891 #

Q: Will clearing the code fix the problem?
A: No. P0891 will return if the root cause (relay, wiring, or TCM fault) is not corrected. Always repair the underlying issue before code clearing.

Q: Is P0891 related to a failing transmission?
A: Not directly. P0891 is an electrical fault in the relay circuit, not a mechanical transmission failure. However, it can cause shifting problems if not fixed.