P0099–P00A9 Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic Bank 1
The fault comes and goes, which points at a connection that only breaks under vibration, heat or load.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P0099 | Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic Bank 1 | Investigate soon |
P00A9 | Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic Bank 2 | Investigate soon |
The definition
P0099: Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic Bank 1.
P0099 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
- Check the connector at the part for corrosion, and that it is fully seated.
- Clear the code and see whether it returns, and under what conditions.
What actually causes this on a VAG
Intake air temperature sensor 2 is the one measuring air after the turbocharger and charge air cooler; on many VAG engines it's built into the charge pressure sensor in the manifold or charge pipe. Sensor 1 is the one further upstream near the air filter. "Intermittent/erratic" means the signal is jumping around in a way real air temperature can't - dropping out for an instant, spiking, then coming back - so the ECU stops trusting it and uses a substitute figure. Air temperature changes gradually; electrical connections fail suddenly, which is why this wording points at a connection or a wire far more often than at the sensor. You may notice nothing at all, or occasional flat spots and slightly reduced boost while it's running on the substitute.
Most likely causes, in order
- Connector fault at the sensor. Moisture in the plug, corroded or spread terminals, or a snapped locking tab that lets the connector creep loose under vibration. With the engine idling and the sensor's live value on screen, wiggle the plug and the loom behind it - a reading that jumps or drops out as you move it is your answer, and costs nothing to find.
- Chafed harness making intermittent contact. Check where the loom crosses the intake manifold, brackets and any edge it can rub against, and anywhere it flexes as the engine moves on its mounts. Heat hardens the insulation over years and vibration then wears through it. This kind of fault often shows up on rough roads or under load rather than sitting at idle, so a log taken on the road is worth far more than one taken on the drive.
- The sensor itself failing. A cracked sensor body or a breaking-down element can produce a jumpy signal with a perfectly good plug and loom. Treat this as the answer only after the connector and the accessible wiring have been checked and cleared. A caked, oily or sooty element is worth noting if you find one - engines that breathe oil mist back into the inlet, and diesels routing soot through the EGR, do coat these sensors - but that kind of contamination usually makes a sensor slow and drifty rather than jumpy, so it fits a plausibility code better than this one. On engines where the element is part of the charge pressure sensor there is nothing separately serviceable to clean anyway.
Worth knowing: There's a free test worth doing before anyone touches a spanner. On a car that has stood overnight, every intake air temperature sensor and the ambient air sensor should read within a few degrees of each other and of the actual outside air - allow a little extra if the car has been in a warm garage. If they all agree when cold, the sensor is honest and you are looking for a connection or a wire. It's also worth logging this sensor while driving the conditions that set the code: a value that snaps to an extreme and back in an instant is electrical, while one that wanders slowly is more likely a genuine or drifting temperature, and that's a completely different repair.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P0099 mean?
P0099 means Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic Bank 1. The fault comes and goes, which points at a connection that only breaks under vibration, heat or load.
Can I drive with P0099?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.