Failed intake air heater element (open or shorted internally); Damaged or corroded wiring harness or connector at the heater; Blown fuse or faulty relay in the intake air heater circuit; Poor ground connection for the heater circuit; Faulty intake air temperature sensor providing incorrect data to the ECM; ECM internal driver failure (less common)

DTC codes / P06xx · Computer and output circuits / P0640

P0640Intake Air Heater Control Circuit

Q: What does code P0640 mean?

Intake Air Heater Control Circuit. P0640 indicates that the engine control module (ECM) has detected a fault in the electrical circuit controlling the intake air heater, which is a grid or element that warms incoming air on certain diesel engines to aid cold starting and reduce white smoke. The ECM monitors the circuit for expected voltage or current and sets the code when the signal falls outside the normal range, often due to an open circuit, short, or failed heater element.

P0640 indicates that the engine control module (ECM) has detected a fault in the electrical circuit controlling the intake air heater, which is a grid or element that warms incoming air on certain diesel engines to aid cold starting and reduce white smoke. The ECM monitors the circuit for expected voltage or current and sets the code when the signal falls outside the normal range, often due to an open circuit, short, or failed heater element.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Hard starting or rough idle when the engine is cold, especially in low ambient temperatures
Excessive white smoke from the exhaust after a cold start
Reduced engine performance or poor fuel economy during warm-up
In rare cases, a no-start condition in very cold weather if the heater is completely inoperative

Common causes, most likely first

Failed intake air heater element (open or shorted internally)
Damaged or corroded wiring harness or connector at the heater
Blown fuse or faulty relay in the intake air heater circuit
Poor ground connection for the heater circuit
Faulty intake air temperature sensor providing incorrect data to the ECM
ECM internal driver failure (less common)

How to diagnose and fix it

Scan all modules for stored codes and freeze-frame data to confirm P0640 is active and not history
Visually inspect the intake air heater, its connectors, and wiring for damage, corrosion, or loose connections
Check the fuse and relay associated with the intake air heater circuit and replace if faulty
Measure resistance of the heater element with a multimeter and compare to manufacturer specifications
Test for voltage and ground at the heater connector with the key on and during commanded heater activation
Perform a voltage drop test on the power and ground circuits to identify excessive resistance
If all external circuits test good, follow the diagnostic flow chart to test the ECM driver or command the heater on with a scan tool and observe current draw

Intake Air Heater Circuit Quirks

Many vehicles set P0640 only in cold ambient temperatures when the ECM commands the heater on, so the code may not reappear in warm weather and can be mistaken for a intermittent fault.
A failed intake air heater often does not affect driveability in mild climates, leading owners to ignore the code until winter starting problems appear.
Corrosion inside the heater connector pins is a frequent cause that can mimic a failed heater element, so always inspect connectors before replacing parts.
The intake air heater circuit is sometimes confused with the glow plug circuit, but they are separate systems; P0640 does not indicate glow plug faults.
On some vehicles, a weak battery or charging system fault can cause the ECM to disable the heater and set P0640 as a secondary code, so check system voltage first.

Can I keep driving with P0640?

You can generally continue driving with P0640, but cold-start performance and emissions may be affected, and in freezing conditions the engine may be harder to start. Avoid extended driving in very cold weather without addressing the fault, and have the circuit inspected before winter.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.