The P0640 code in your 2022 GMC Terrain indicates a malfunction in the intake air heater control circuit. The intake air heater is designed to warm incoming air during cold starts, improving combustion and reducing emissions during the warm-up period. When the control circuit fails, this function is compromised.
Intake Air Heater Function
Your Terrain's intake air heating system warms the air entering the engine during cold conditions. By increasing air temperature, fuel vaporization improves and combustion becomes more complete. This reduces cold-start emissions and can improve drivability until the engine reaches normal operating temperature. The ECM controls when and how the heater operates.
Why This Code Appears
A failed intake air heater element is a common cause—the heating element burns out over time. Wiring issues between the ECM and heater, including opens, shorts, or corrosion, affect control. The relay that powers the heater may have failed. In some cases, the ECM's heater control driver circuit has malfunctioned. Poor grounds at the heater or relay also cause control issues.
Symptoms You May Notice
Cold start issues including rough running during warm-up may occur. The check engine light illuminates with P0640 stored. In most cases, once the engine warms up, operation normalizes. You might notice slightly increased emissions during cold starts. In warm climates, symptoms may be minimal since the heater isn't used as often.
Diagnostic Approach
Using GM GDS2, command the intake air heater on and monitor circuit response. Measure voltage at the heater connector when commanded—proper voltage indicates the circuit up to that point is good. Test the heater element for continuity to verify it hasn't burned out. Check the relay for proper operation. Inspect wiring for damage between components.