Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
Your car's computer is getting a signal that a part controlling the transmission power is too high. It's like a light bulb getting too much electricity.
The Transmission Control Module (TCM) monitors the power relay circuit to ensure it is operating within the expected range. If the voltage is higher than expected, the code P0891 is set.
The P0891 code indicates that the TCM has detected an unusually high voltage in the power relay sense circuit. This could be due to a fault in the relay, wiring issues, or a malfunctioning TCM.
• Check Engine Light is on
• Transmission may not shift properly
• Vehicle may go into 'limp' mode
• Faulty TCM power relay
• Wiring issues or short circuits
• Defective TCM
TCM: Transmission Control Module
Relay: An electrically operated switch
• Scan the vehicle for codes and note any additional codes.
• Inspect the TCM power relay and wiring for damage.
• Test the relay circuit voltage with a multimeter.
• Replace the TCM power relay if faulty.
• Repair or replace damaged wiring.
• Replace the TCM if it is defective.
• OBD-II scanner
• Multimeter
• Basic hand tools
$100 - $500
Moderate
• Ford F-150
• Chevrolet Silverado
• Dodge Ram
• Regularly inspect electrical connections.
• Keep the vehicle's electrical system in good condition.
• Perform routine maintenance checks.
Electrical Issue
• Avoid driving long distances until the issue is resolved.
• Consult with a professional mechanic for accurate diagnosis.
Check with your vehicle's manufacturer for warranty coverage on electrical components.
This code has been associated with electrical issues in vehicles with aging wiring or faulty relays.
Moderate – It is recommended to address this issue soon to avoid potential transmission problems.
Driving with a malfunctioning transmission can be unsafe. Address the issue promptly.
• Engine running
• Transmission in park or neutral
The TCM power relay is typically located in the vehicle's fuse box or near the transmission.
Q: Can I drive with a P0891 code?
A: It's not recommended as it may affect transmission performance.
Q: Is a P0891 code serious?
A: Yes, it can lead to transmission issues if not addressed.
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