P0885
UniversalThe Transmission Control Module (TCM) Power Relay Control Circuit is open, meaning there is no electrical connection or an interruption in the circuit that supplies power to the TCM via its control relay.
High SeverityThis code indicates an electrical issue where the Transmission Control Module (TCM) is not receiving proper power due to an open circuit in its power relay control. This can prevent the transmission from shifting correctly or at all, making the vehicle undrivable.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before performing any electrical work on your vehicle. Be cautious when working around hot engine components and moving parts. If the transmission is behaving erratically, do not drive the vehicle as it could cause further damage or lead to an accident.
Common Symptoms
- Check Engine Light illuminated
- Transmission not shifting
- Vehicle stuck in one gear (limp mode)
- Harsh shifting
- No power to the transmission (vehicle will not move)
- Engine may not start (if TCM is part of start circuit interlock)
Common Causes
- Faulty TCM power relay
- Open or shorted wiring in the TCM power relay control circuit
- Corroded or loose electrical connections at the relay or TCM
- Blown fuse related to the TCM power supply
- Faulty Transmission Control Module (TCM) itself
- Damaged relay control circuit within the PCM/ECM (less common)
Frequently reported on: General/Universal
Diagnostic Steps
- Check for blown fuses related to the transmission or TCM in both the under-hood and cabin fuse boxes.
- Locate the TCM power relay (refer to your vehicle's service manual for its exact location) and inspect its terminals for corrosion or damage.
- Test the TCM power relay. You can often swap it with a known good, identical relay from another non-critical system (like the horn or a different fan relay) for testing purposes.
- Inspect the wiring harness connected to the TCM power relay and the TCM itself for any visible signs of damage, fraying, or loose connections.
- Use a multimeter to check for continuity in the relay control circuit and ensure proper voltage is reaching the relay and the TCM.
👨🔧 When to Call a Professional
If you lack experience with electrical diagnostics or if replacing the TCM power relay does not resolve the issue, it is best to consult a professional mechanic. Complex wiring issues or a faulty TCM may require specialized tools and expertise.
Commonly Asked Questions
What is the TCM power relay?
The Transmission Control Module (TCM) power relay is an electrical switch that provides power to the TCM, which controls the vehicle's automatic transmission.
Can I drive with a P0885 code?
It is not recommended to drive with a P0885 code, as it often means the transmission is not functioning properly, potentially leading to further damage or unsafe driving conditions.
Where is the TCM power relay located?
The location of the TCM power relay varies by vehicle make and model. Consult your vehicle's owner's manual or a service manual for the exact location, usually in a fuse box under the hood or inside the cabin.
Is it possible for this code to be caused by a faulty PCM/ECM?
While less common, the PCM (Powertrain Control Module) or ECM (Engine Control Module) can sometimes be responsible for controlling the TCM power relay. If all other components check out, the PCM/ECM may need further diagnosis.
How much does it cost to fix a P0885 code?
The cost to fix a P0885 code can vary widely. If it's just a faulty relay or fuse, it could be under $50. If it involves complex wiring repair or a new TCM, costs can range from a few hundred to over a thousand dollars.