What P0891 means
Some transmissions draw their power through a relay, such as the transmission control relay in Chrysler's fuse box that feeds the solenoids.
How the engine computer detects it
P0885 to P0887 cover the coil control of that relay, P0888 to P0892 its sense line, which reads back the switched output and compares it with the command. A dead relay leaves all solenoids without power, so the transmission drops into its hydraulic emergency gear. P0891 means voltage is present at the relay output although the relay is off: a stuck or welded contact or a back-feed. The module then cannot switch the solenoids off for a safe emergency gear, and it may stay powered after key-off and drain the battery. No maker documents the code.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- MIL on
- Battery drains overnight
- Module stays awake after key-off
Common causes
- Relay contact welded or sticking Most likely
- Sense or output line shorted to voltage Possible
- Wrong relay fitted Less likely
How to diagnose P0891
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: transmission relay, relay wiring, fuse, transmission control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 8
- Transmission
- 91
- Specific fault
Questions drivers ask
Can I drive with code P0891?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0891?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0891 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0891 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.