P0074 Ambient Air Temperature Sensor Circuit Intermittent

OBD-II DTC Datasheet

Ambient Air Temperature Sensor Circuit Malfunction

What does this mean?

This generic transmission / engine DTC usually applies to all OBDII equipped vehicles.

The ambient air temperature (AAT) sensor converts the ambient temperature into an electrical signal to the powertrain control module (PCM). This input is used to change the operation of the air conditioning system and display the outdoor temperature.

PCM gets this input and possibly two more; Intake air temperature (IAT) and engine coolant temperature (ECT) sensor. The PCM checks the AAT sensor voltage and compares it to the IAT / ECT sensor reading when the ignition is first turned on after a long cool-down period. This code is set if these inputs differ too much. It also checks the voltage signals from these sensors to determine if they are correct when the engine is fully warmed up. This code is usually set due to electrical problems.

Troubleshooting steps may vary depending on manufacturer, AAT sensor type, and wire colors.

symptoms

Symptoms may include:

Fault indicator light is on
The air conditioner may not work properly
The instrument cluster may not read the outside temperature accurately
Top console may not read ambient temperature accurately

reasons

Possible causes of DTC P0074 may include:

Intermittent open in signal circuit to AAT sensor - likely
Intermittent short to voltage in the signal circuit of the AAT sensor
Intermittent short to ground in signal circuit to AAT sensor
Defective AAT sensor
Failed PCM – Unlikely

Possible solutions

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

Then find the AAT sensor on your specific vehicle. This sensor is usually located in front of the radiator behind the grille or in the front bumper area. Once detected, visually inspect the connectors and wiring. Look for scratches, scuffs, exposed wires, burn marks, or molten plastic. Disconnect the connectors and carefully inspect the terminals (metal parts) inside the connectors. See if they look burnt or have a green tint indicating corrosion. If you need to clean the terminals, use an electrical contact cleaner and a plastic bristle brush. Allow to dry and apply electrical grease where the terminals touch.

The most common fault is connections, with a faulty sensor coming in second place due to adverse environmental conditions.

When checking the connections, you can check the sensor using a digital volt ohm meter (DVOM). Ignition OFF, disconnect the sensor and connect the red (positive) DVOM terminal to one terminal on the sensor and the black (negative) DVOM terminal to the other terminal. Determine the temperature of the sensor (what is the temperature outside) by the resistance according to the table. This is the ohm resistance that your DVOM should display. Either 0 ohms or infinite resistance (usually indicated by the letters OL) indicates a faulty sensor.

If you have a scan tool, clear the diagnostic trouble codes from memory and see if the code returns. If this is not the case, then there is most likely a connection problem.

If the P0070 code does return, we will need to test the AAT sensor and associated circuits. Usually there are 2 wires on the AAT sensor. Ignition OFF, disconnect the harness at the AAT sensor. Switch on the ignition. With a scan tool accessing the PCM data (assuming it is a module receiving AAT sensor input; the module receiving AAT sensor input could be the air conditioning control module, universal electronic module, or some other module towards the front vehicle that can send AAT sensor data over the bus network), read the temperature or voltage of the AAT sensor. It should show 5 volts or something other than the ambient temperature (very low temperature) in degrees. Next, turn off the ignition, connect a jumper wire to the two terminals inside the harness connector going to the AAT sensor, then turn the ignition on. It should read about 0 volts or something other than the ambient temperature (very high temperature) in degrees. If there is no 5 volt on the sensor or you see no change, repair the wiring from the PCM to the sensor, or possibly a faulty PCM.

Reconnect the sensor and wiggle the connector while monitoring the voltage or degrees from the AAT sensor. If, while wiggling the wires, a change is detected in any of them, this indicates an intermittent connection. Look for where the wires are routed and mark any point where they might touch / rub against the body panel or frame.

If all previous tests pass and you continue to receive P0070, it will most likely indicate a failed AAT sensor, although the failed control module cannot be ruled out until the AAT sensor is replaced. If you are unsure, seek help from a qualified automotive diagnostician. To install correctly, the PCM must be programmed or calibrated for the vehicle.

Related DTC discussions

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