Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Chart B-1 - Coolant Temperature Light Diagnosis
COOLANT TEMP light is powered by ignition circuit No. 39 through GAGES fuse. BCM supplies ground to circuit No. 35 (BCM terminal "A6") to illuminate COOLANT TEMP light when coolant temperature is greater than 257°F (125°C). Coolant temperature data is sent by PCM to BCM through circuit No. 526 (PCM-BCM serial data).
- Verifies integrity of IPC, bulb and circuits No. 35 and 39. If bulb comes on when circuit No. 35 is jumpered to ground at BCM, bulb, IPC and associated wiring are okay. Problem may be a faulty BCM connection or BCM.
- Ensures circuit No. 39 is supplying ignition feed to indicators.
- Determines whether problem is an open in circuit No. 35, IPC, bulb or connector.
- Checks if circuit No. 35 is grounded or if IPC is faulty.
- Ensures BCM is not receiving data indicating an overheat condition from PCM. If BCM data P.2.1 displays a coolant temperature greater than 257°F (125°C), problem is in either coolant sensor circuit or engine cooling system.
- Check cooling system as necessary.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.