The P0070 error code is a common diagnostic trouble code (DTC) in vehicles equipped with OBDII systems, and sometimes referred to as EOBD in European models. This code signals an issue within the Ambient Air Temperature (AAT) sensor circuit. As an expert auto repair content creator for autelfrance.com, I’ll break down what this code means, its symptoms, potential causes, and how to diagnose and fix it, ensuring your readers get the most helpful and SEO-optimized information.
What is the OBDII P0070 Code?
The OBDII (On-Board Diagnostics II) system is used in most modern vehicles to monitor various systems and components. When your vehicle’s Powertrain Control Module (PCM) detects a problem in the Ambient Air Temperature (AAT) sensor circuit, it sets the P0070 trouble code.
The AAT sensor plays a crucial role by measuring the outside air temperature. This information is then relayed to the PCM, which uses it for several functions, most notably to optimize the performance of the air conditioning system and to accurately display the outside temperature on your vehicle’s dashboard or overhead console.
The PCM constantly monitors the AAT sensor’s readings, comparing them with other temperature sensors like the Intake Air Temperature (IAT) sensor and Engine Coolant Temperature (ECT) sensor. When the vehicle is first started after a cooldown period, the PCM expects these temperature readings to be relatively similar. A significant discrepancy between these sensors, or incorrect voltage signals when the engine is warm, can trigger the P0070 code.
This trouble code often points to electrical problems within the AAT sensor circuit rather than a sensor malfunction itself. Understanding this is key to effective troubleshooting.
Symptoms of a P0070 Code
When the P0070 code is present, you might notice several symptoms in your vehicle:
- Malfunction Indicator Light (MIL) or Check Engine Light is on: This is the most immediate and common symptom, alerting you to a problem within the engine management system.
- Air Conditioning System Malfunctions: The A/C might not cool as effectively as it should, or it may not function at all. The PCM uses AAT data to optimize A/C operation, and incorrect readings can disrupt this.
- Inaccurate Outside Temperature Readings: The temperature displayed on your instrument cluster or overhead console might be incorrect or completely absent.
- Potential Impact on Engine Performance: In some less common cases, although primarily related to temperature readings for comfort and A/C, extreme incorrect AAT readings could theoretically influence minor engine management strategies, though this is less direct.
These symptoms can vary in severity, but the presence of the P0070 code indicates a definite issue requiring diagnosis.
Common Causes of a P0070 Error
Several factors can lead to the P0070 trouble code. Pinpointing the exact cause is crucial for a successful repair:
- Open Circuit in the Signal Wire to the AAT Sensor: A break in the wiring can prevent the signal from reaching the PCM. This is a frequent culprit, often due to damage from road debris, animals, or wear and tear.
- Short to Voltage in the Signal Wire: The signal wire might be inadvertently contacting a voltage source, sending an incorrect signal to the PCM.
- Short to Ground in the Signal Wire: The signal wire may be shorting to ground, again disrupting the correct signal transmission.
- Faulty AAT Sensor: While less common than wiring issues, the AAT sensor itself can fail. This is often due to environmental exposure and temperature fluctuations.
- PCM Failure (Unlikely): Although possible, a failed PCM is the least likely cause. PCM issues are generally considered after ruling out all other potential problems.
- Corroded or Damaged Connectors: The electrical connectors at the AAT sensor or along the wiring harness can become corroded or damaged, leading to poor electrical contact.
Understanding these potential causes helps in systematic troubleshooting to resolve the P0070 code.
Diagnosing and Fixing the P0070 Code
Diagnosing a P0070 code requires a methodical approach. Here’s a step-by-step guide to help you pinpoint and fix the issue:
1. Preliminary Checks and TSBs:
Begin by checking for any Technical Service Bulletins (TSBs) issued by your vehicle’s manufacturer related to the P0070 code. TSBs can provide valuable information about known issues and specific fixes for your vehicle model, potentially saving you time and effort.
2. Visual Inspection of Wiring and Connectors:
Locate the AAT sensor. It’s typically positioned at the front of the vehicle, often behind the grille or front bumper, in front of the radiator to measure ambient air accurately.
Alt text: Location of the Ambient Air Temperature Sensor behind the grille of a vehicle, highlighting typical placement for accurate ambient air measurement.
Carefully inspect the wiring and connectors leading to the AAT sensor. Look for:
- Physical Damage: Check for scraping, rubbing, cuts, or bare wires.
- Melted or Burned Components: Look for signs of overheating or electrical shorts.
- Connector Condition: Disconnect the connectors and examine the terminals inside. Check for corrosion (greenish tint), bent pins, or damage. Clean corroded terminals with electrical contact cleaner and a plastic brush. Apply dielectric grease after cleaning to prevent future corrosion.
3. Sensor Resistance Test:
Use a Digital Volt-Ohm Meter (DVOM) to test the AAT sensor’s resistance.
- Disconnect the sensor.
- Set your DVOM to measure resistance (Ohms).
- Connect the DVOM leads to the sensor terminals.
- Compare the measured resistance with the expected value based on the ambient temperature. Sensor resistance values typically change with temperature; you might need to consult a repair manual or online resources for a temperature-resistance chart specific to your vehicle’s AAT sensor.
- An open circuit (infinite resistance or “OL” on the DVOM) or a very low resistance (close to 0 ohms) often indicates a faulty sensor.
Alt text: Using a Digital Volt-Ohm Meter (DVOM) to measure the resistance of an Ambient Air Temperature Sensor, a crucial step in diagnosing a P0070 code.
4. Circuit Voltage Test:
Check for proper voltage supply to the AAT sensor circuit.
- Disconnect the AAT sensor.
- Turn the ignition key to the “ON” position (engine off).
- Use a scan tool to access PCM data and read the AAT sensor voltage or temperature reading. If you cannot access data, use the DVOM to check for voltage at the sensor connector on the harness side. You should typically see around 5 volts (reference voltage from the PCM).
- If there’s no voltage, there’s likely an open circuit or a PCM issue.
5. Signal Circuit Test:
Test the signal wire for shorts or opens.
- With the ignition off, disconnect the AAT sensor.
- Using a jumper wire, connect the two terminals in the harness connector that goes to the AAT sensor.
- Turn the ignition to the “ON” position.
- Use a scan tool to read the AAT sensor voltage or temperature again. It should now read close to 0 volts or indicate a very high temperature, which signifies the signal circuit is responding to the change (jumper effectively simulating a very low resistance sensor reading).
- If there’s no change in reading, suspect a problem in the signal wire between the sensor connector and the PCM or the PCM itself.
6. Scan Tool Code Clearing and Re-Test:
After performing any repairs or component replacements:
- Use a scan tool to clear the P0070 DTC from the PCM memory.
- Take the vehicle for a test drive under conditions that previously triggered the code.
- Rescan the system to see if the P0070 code returns.
If the code does not return, the issue is likely resolved. If it reappears, further diagnosis, potentially involving more in-depth wiring checks or PCM testing, may be necessary.
7. Consider Professional Assistance:
If you’ve performed these steps and are still facing the P0070 code, or if you are uncomfortable with electrical testing, it’s advisable to seek assistance from a trained automotive diagnostician. Modern vehicle systems can be complex, and professional tools and expertise can be invaluable for accurate diagnosis and repair. Remember that PCMs, if replacement is needed (rare), often require programming to match your specific vehicle.
Conclusion
The OBDII P0070 code indicates a problem within the Ambient Air Temperature Sensor circuit. While the symptoms might seem minor, addressing this issue is important for the optimal functioning of your vehicle’s air conditioning and diagnostic systems. By following a systematic diagnostic approach, starting with visual inspections and moving to electrical testing, you can effectively troubleshoot and resolve the P0070 code. Remember to prioritize safety when working with electrical systems and consult professional help when needed.
