P2682

Symptoms

• Check engine light or coolant-temperature warning lamp
• engine temperature climbing faster than normal (with a stuck-closed valve the gauge can reach the red zone within minutes of driving)
• weak or absent cabin heating because the heater core receives insufficient hot coolant
• if the valve fails stuck-open
• engine over-cooling at cold start
• reduced fuel economy and related codes such as P0128.

Probable causes

• Internal valve solenoid coil shorted from heat cycling
• vibration or coolant contamination (most common)
• coolant seepage into the electrical connector causing corrosion and short-to-ground
• control wire chafed against the engine block
• exhaust or chassis creating a short-to-ground
• failed PCM driver transistor or damaged circuit board trace (rare)
• PCM software calibration error
• harness damage from heat or rodents.

Diagnostic steps

1. Retrieve the code and freeze-frame data with a scan tool and document the coolant temperature at the time the code set.
2. Visually inspect the bypass valve connector and harness for coolant intrusion, green corrosion, chafed insulation and rodent damage; check for coolant leaks near the valve.
3. Measure the control circuit voltage and ground continuity per service data (one source specifies approximately 5V +/- 0.5V on the control circuit).
4. Bench-test the valve by applying direct battery voltage (12V) to the valve coil to confirm it actuates.
5. If the circuit and valve test good, monitor the PCM driver output with an oscilloscope to confirm output integrity.
6. Check manufacturer service bulletins for applicable PCM software updates.
7. Repair wiring, replace the valve, or address the PCM based on findings, then clear the code and verify normal warm-up behavior.