P0070
PowertrainAmbient Air Temperature Sensor Circuit
The ECU keeps an eye on the little outside air temperature sensor by reading the voltage on its circuit. When that voltage drops out, sticks at an impossible value, or shorts away, the ECU knows the reading can't be real and logs P0070. For you, this usually shows up as a dashboard temperature display gone haywire and the climate control behaving oddly. It's a low-stress fault that rarely affects how the car drives, but it does want sorting because it touches the air con and the mixture on cold mornings.
ⓘ Information only. This page provides general educational information about fault code P0070. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0070 mean?
P0070 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Ambient Air Temperature Sensor Circuit.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, often with no change in how the car feels to drive
- • Outside temperature on the dash frozen, blank, or showing something daft like -40
- • Climate control or air con struggling to hold the cabin temperature you've set
- • Slightly worse fuel economy, usually only a couple of percent and easy to miss
- • A bit of hesitation or rough running on a cold start, then it clears once warm
Possible causes
Causes commonly associated with P0070, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. The ambient air temperature sensor itself has failed, by far the usual culprit. They sit in harsh weather and eventually pack in
- 2. Corroded or loose connector at the sensor, very common in the UK thanks to winter road salt working into the plug
- 3. Damaged wiring near the front of the car, the sensor often lives behind the grille or in the bumper where stone chips and minor knocks reach it
- 4. Water sitting in the connector or sensor housing, shorting the signal after a wet spell
- 5. An open circuit, short to ground, or short to voltage somewhere along the signal wire to the ECU
- 6. A failed engine control module, which is rare and the last thing to suspect after everything else checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Plug in a scanner and read the live ambient temperature value alongside the code. If it's pinned at -40 or some silly figure while it's a mild 12 degrees outside, you've confirmed the sensor or its wiring is the problem before you touch a spanner
- 2. Find the sensor. On most UK cars it's tucked behind the front grille or in the lower bumper, and on a few it lives in the passenger door mirror
- 3. Pull the connector and look closely for green corrosion, bent pins, a cracked seal, or damp inside the plug. This is where most of these faults hide
- 4. With the ignition on and engine off, back-probe the signal wire with a multimeter. You're looking for a sensible voltage that shifts as the temperature changes, anywhere in the roughly 0.1 to 5 volt range depending on the system
- 5. Check continuity and resistance back to the ECU and repair any breaks, shorts, or dodgy connections you find
- 6. If the wiring is clean and the readings are still nonsense, fit a new sensor, clear the code, and take it out to confirm it stays off
Common questions about P0070
How do I know if it's the sensor or just the wiring and plug? +
Start at the connector, because UK winters fill these plugs with salty grime and that fakes a sensor fault all the time. Unplug it and check for corrosion or water. If the pins are clean and dry, back-probe the signal wire with the multimeter and see if the voltage moves with temperature. A reading that's dead or stuck means either the wire or the sensor, so test continuity back to the ECU to split the two. A clean circuit with a frozen reading points the finger at the sensor itself.
How long should this take to fix? +
If it's just the sensor, you're looking at well under an hour at a garage once they've located it. The diagnosis is usually the longer part of the job. Wiring repairs are where the clock runs, tracing a damaged loom or rebuilding a corroded connector can take an hour or two on its own depending on how buried the cable is behind the bumper.
Is a cheap aftermarket sensor okay or should I pay for genuine? +
For most everyday cars a decent quality aftermarket sensor from a known brand is fine and saves you a fair bit over the dealer part. Avoid the bargain-bin no-name listings, they're known for reading a few degrees out or failing again within a year, which defeats the point. If you've got a newer car with a fussy climate system, sticking with OEM or a top-tier aftermarket part saves the aggravation of it logging the code again.
Can I keep driving with this showing? +
Yes, the car will run and drive normally with P0070 logged, so there's no panic. Your air con and outside temp display may misbehave, and you might notice a slightly rougher cold start, but it won't put you in limp mode or leave you stranded. Sort it within a few weeks, mainly so the warning light isn't hiding something more serious that crops up later.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →