Transmission Control Module (TCM) Performance
The TCM is not performing within expected parameters.
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What it means (plain English)
The Transmission Control Module (TCM) is in charge of controlling the transmission. If this code appears, it means the TCM isn't working right, which can affect how the vehicle shifts gears.
What the computer is actually seeing
The TCM monitors inputs like engine speed, vehicle speed, and throttle position to manage gear shifts. If any of these readings are outside of the expected range or if the TCM fails to react properly within 200 milliseconds, this code triggers.
What a healthy reading looks like
Engine speed: 600-4000 RPM, Vehicle speed: 0-120 MPH, Throttle position: 0-100%. All readings should be stable and within this range during typical driving.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check transmission fluid level and condition. Ensure it's clean and at the correct level. If not, correct the fluid issue and retest.
- 22. Inspect wiring and connections to the TCM for corrosion or damage. Repair any issues found.
- 33. Use a scan tool to check for other related trouble codes. If there are other codes, address them first as they may lead to this issue.
- 44. Verify the operation of the vehicle speed sensor (VSS) and throttle position sensor (TPS) using a multimeter or scan tool. Confirm readings are within expected values.
- 55. If all checks are clear and the code persists, consider testing or replacing the TCM.
Common causes
- Faulty Transmission Control Module
- Poor electrical connections or wiring issues
- Incorrect vehicle speed sensor reading
- Malfunctioning throttle position sensor
- Faulty transmission components affecting operation
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It's not recommended to drive for an extended time; shifting may be compromised.
Will this code come back after clearing?
It might if the underlying problem isn't resolved.
Why does this code pair with SPN 649?
Both relate to TCM performance and could indicate a shared fault in the transmission system.
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