You probably know that an illuminated Check Engine Light (CEL) means that at least one sensor has sent a reading to the engine's powertrain control module (PCM) that's out of spec, registering a trouble code. You also most likely know that you can access the trouble codes that are stored in the PCM by using a scanner, hooked up to the diagnostic connector under the dash.
The introduction of standardized OBD-II codes across all makes/models of vehicles has made troubleshooting much easier. Rather than relying on intuition, deduction and experience, the trouble codes are designed to point you in the right direction.
Where it gets tricky, though, is interpreting what the codes mean. Sometimes it's just a matter of the sensor itself being faulty, but most of the time there's some other condition that has caused a trouble code to register. Also, bear in mind that sometimes a single problem can trigger several trouble codes and there will be a certain amount of reading between the lines to determine what's really at play.
P0070 Ambient Air Temperature Circuit: What It Means
The temperature of air that enters the engine has an effect on fuel metering, since cold air is more dense than warm air (hence the popularity of cold-air intakes as a performance mod).
The ambient air temperature sensor informs the PCM of its temperature readings, and the PCM can then strike a balance between intake air temperature and ambient air temperature for fuel delivery. The ambient air temp sensor is also used as a reference by the PCM, related to other temp sensors on the engine.
A P0070 code is stored when the PCM detects that ambient air and intake air temperatures are out of spec, illuminating the CEL.
NOTE: Other ambient air temp sensor codes can include P0071 (ambient air temp sensor range/performance), P0072 (ambient air temp sensor low input) and P0073 (ambient air temp sensor high input).
Symptoms
In some cases, there are no symptoms other than an illuminated CEL. Often, though, it can result in a climate control/HVAC system that doesn't perform properly.
What Happens If I Ignore It?
If you ignore a P0070 code, you may eventually see a hard-start condition and your vehicle could fail emissions tests.
Possible Fixes
- Locate the ambient air temperature sensor on the engine (this can vary greatly from one year/make/model to another but many are located behind the grille, near the AC condenser).
- Inspect the wires going to the sensor and make sure there's no corrosion or loose/broken wires or connectors.
- Ensure there's nothing physically blocking the sensor - the location of this part makes it vulnerable to impact and even the smallest fender-bender can be enough to cause a malfunction.
- If everything looks good, use the device to clear the code and then test drive the vehicle.
- If the P0070 code comes back again right away, replace the sensor.
- If the P0070 code comes back later, there's a chance that there's an intermittent problem with the voltage going to the PCM.
- While rare, this problem could point to an underlying issue and could be accompanied by other trouble codes
As with any other OBD-II related troubleshooting, diagnosis and repair, remember that your problem could be a common one for your year/make/model of vehicle. It's a good idea to look for technical service bulletins (TSBs), recalls or any other information you can find before popping the hood and turning wrenches.
Have you ever had this code come up when working on your car?
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About the Author(s)
Jerry Renshaw is a veteran journalist, gearhead and guitar player, and cultivated his mechanical skills by 30 years of turning wrenches to keep one piece of junk or another on the road. He's owned everything from a Chevette to (three) minivans to a fire-breathing Dodge muscle truck, and is constantly keeping up to speed on what's going on in the automotive world.
