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P0640 OBD-II Trouble Code: Intake Air Heater Control Circuit

check engine light

P0640 code definition

When your vehicle’s PCM stores a P0640 code, it means that abnormal input voltage

has been identified as coming from the intake air heater’s control circuit.

What the P0640 code means

This means that a voltage that exceeds the level stipulated by the manufacturer has

occurred. Usually, your Check Engine Light will come on, although sometimes the code

has to be recorded three times before this happens.

What causes the P0640 code?

Most often, the P0640 code is recorded when the intake air heater relay is faulty. There

can be other causes as well, though, including:

What are the symptoms of the P0640 code?

Most of the time, there are no symptoms at all other than the Check Engine Light coming

on. You may, however, notice some loss in fuel efficiency, since the intake air heater

system works to warm the air entering the engine. If the air getting to the engine isn’t

warm enough, then you may notice a bit of a dip in your fuel economy.

Sometimes, the problem is not the intake air heater relay. Your Check Engine Light

could come on just because you have a dirty air filter.

How does a mechanic diagnose the P0640 code?

First off, your mechanic will use an OBD-II scanner and an ohmmeter to identify any

conditions that may result in a code being recorded. Next, your mechanic will:

  • Visually inspect all the wiring and connectors

  • Repair or replace any damaged wiring and connectors

  • Re-test your vehicle’s system to make sure that the replacements did the job and that everything is in proper working order

  • Connect the scanner again to make sure that the codes are no longer active

  • Test drive the car to see if the codes re-appear

  • Crank the engine and check the scanner again to make sure that the heater turns on

  • Ensure that the blower is working

  • Compare the findings with the vehicle manufacturer’s specifications

Common mistakes when diagnosing the P0640 code

Sometimes, mechanics fail to make sure that intake air temp sensors are properly

connected. This can cause a code to be improperly stored. Mechanics are also

sometimes too quick to blame the PCM itself for the problem, but the reality is that the

PCM hardly ever fails.

How serious is the P0640 code?

This is something that you can have repaired at you leisure. You may notice a slight

decrease in your engine performance, and you may also find that you are paying a little

more at the pump than you are accustomed to. However, this is not an issue that is

going to compromise your safety, or that of anyone who travels with you. It would be

a good idea to get the problem corrected, but if you have other things to do (as most of

us have), you can wait for a more convenient time.

What repairs can fix the P0640 code?

Sometimes all that is needed is to replace a dirty air filter. Other times, though, you may

need to have one or more of the intake air sensors replaced. Either way, this is not a

major maintenance or repair issue, and can be easily and economically dealt with by a

qualified mechanic.

Additional comments for consideration regarding the P0640 code

Any voltage variation that is outside the manufacturer’s specifications can lead to a

P0570 code. It doesn’t necessarily mean that anything is terribly wrong, though.

Need help with a P0640 code?

YourMechanic can assist you with any problems that relate to fuel economy, or any

other problems that you may have with your vehicle. Our qualified mechanics are

always on standby, ready to go to your home or office to help you with whatever issues

you may be having. Call us at 1-800- 701-6230, or use our online form to arrange a

visit. Our mechanics are here for you.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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