PCM/ECM/TCM Internal Temperature Sensor Circuit High
P0669 indicates the PCM/ECM/TCM internal temperature sensor circuit is reading higher than expected. This sensor monitors the control module's internal temperature to prevent overheating and ensure proper operation. When the voltage signal exceeds the normal range, the code sets to alert you to a potential electrical or sensor malfunction.
What You Might Notice
- Check engine light illuminated
- Engine will not start or difficulty starting
- Engine stalling or stumbling
- Improper transmission shifting or harsh shifts
- Transmission warning lamp illuminated
Most Common Causes
- 1
Corroded or damaged connector
Corrosion or physical damage to the PCM/ECM/TCM connectors can cause poor electrical contact, leading to false high temperature readings. This is the most common cause and should be inspected first.
- 2
Faulty PCM/ECM/TCM internal temperature sensor
The internal temperature sensor within the control module may be defective, stuck, or degraded, causing it to report incorrectly high values to the system.
- 3
Loose or defective control module ground strap
A loose, corroded, or damaged ground connection between the control module and vehicle chassis causes voltage reference errors that can trigger high temperature fault codes.
- 4
Faulty or damaged wiring
Broken, shorted, or damaged wiring between the control module and related circuits can create signal integrity issues and voltage anomalies interpreted as overtemperature conditions.
How to Diagnose It
- 1
Check Corroded or damaged connector — Corrosion or physical damage to the PCM/ECM/TCM connectors can cause poor electrical contact, leading to false high temperature readings. This is the most common cause and should be inspected first.
- 2
Check Faulty PCM/ECM/TCM internal temperature sensor — The internal temperature sensor within the control module may be defective, stuck, or degraded, causing it to report incorrectly high values to the system.
- 3
Check Loose or defective control module ground strap — A loose, corroded, or damaged ground connection between the control module and vehicle chassis causes voltage reference errors that can trigger high temperature fault codes.
- 4
Check Faulty or damaged wiring — Broken, shorted, or damaged wiring between the control module and related circuits can create signal integrity issues and voltage anomalies interpreted as overtemperature conditions.
How to Fix It
- 1
Inspect and clean connector terminals
Locate the PCM/ECM/TCM connectors and inspect for corrosion, bent pins, or loose contacts. Clean terminals with electrical contact cleaner and dielectric grease, then firmly reseat connectors. This resolves most P0669 codes.
- 2
Check and repair ground straps
Inspect the ground strap connecting the control module to the chassis for corrosion, looseness, or damage. Tighten all bolts securely and clean contact points with a wire brush. Replace the strap if damaged or burned.
- 3
Inspect wiring and harness
Visually trace all wiring related to the PCM/ECM/TCM temperature sensor circuit for cuts, abrasion, pinching, or improper routing. Repair or reroute damaged wires and use appropriate splicing or loom protection as needed.
- 4
Replace PCM/ECM/TCM
If connector, ground, and wiring are all intact and clean, the control module itself likely has a failed internal temperature sensor. The entire PCM/ECM/TCM unit will need replacement and may require reprogramming to your vehicle.
Need a deeper diagnosis?
Search for related repair guides or browse by system.