P0885: Transmission Control Module Power Relay Control Circuit/Open
What to do
Two symptoms point here and they look unrelated: shift quality getting gradually worse, and the battery going flat if the car stands for a few days. If either is happening alongside this code, mention it — the relay is inexpensive and both come from it.
What this code means
A fault in the circuit by which the module controls its own power relay. The arrangement is worth understanding because it explains a class of otherwise baffling symptoms: the module energises the relay that supplies it, and holds it energised after the ignition is switched off until it has finished writing its learned values to memory.
That gives two failure modes with nothing in common. A relay released too early cuts the supply mid-write, so adaptations are saved incomplete and shift quality degrades a little more each time the car is switched off. A relay that never releases keeps the module powered continuously and flattens the battery over a few days of standing.
So a car whose shift quality has been deteriorating for no clear reason, and a car with a mysterious overnight battery drain, can be the same fault in opposite directions.
Likely causes
Start here
Less common
- Poor module ground connection · moderate
Rare
- Faulty transmission control module · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0885.