P0099
Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic Bank 1.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 0
- AreaFuel and air metering, auxiliary emission controls
- 99
- FaultThe specific fault in that area
What it means
P0099 is the generic code for an intermittent or erratic signal from intake air temperature sensor 2 on bank 1. The engine control unit saw the sensor's voltage jump or drift in a way that does not match real air temperature changes, or drop out briefly. Sensor 2 is often located after the turbocharger or in the charge air path, but its position depends on the engine.
Symptoms
- Check engine light on
- Hesitation or hesitant pickup under load
- Poor fuel economy
- Rough idle or occasional surging
- Reduced power or limp mode on some turbocharged engines
- Hard starting in some cases
Possible causes
- Loose, corroded or damaged connector at intake air temperature sensor 2likely
- Chafed, broken or intermittently open wiring to the sensor, or a poor signal or reference connectionlikely
- Faulty intake air temperature sensor 2 giving an erratic readinglikely
- Moisture or oil contamination in the connector or sensorpossible
- Wiring running close to a heat source or high-current cable causing interferencepossible
- Poor ground or reference voltage fault at the control unitrare
- Fault inside the engine control unitrare
How to diagnose
- Read all stored codes and freeze frame data to see engine temperature, load and speed when the fault set, and note any other temperature or sensor circuit codes.
- Locate intake air temperature sensor 2 using the model-specific information, as its position varies by engine, then inspect the sensor and connector for damage, looseness, corrosion, moisture or oil.
- Inspect the wiring harness along its full length for chafing, heat damage and tight bends, and gently wiggle the harness and connector while watching the live temperature reading for jumps.
- Compare the live reading of sensor 2 with the other intake air temperature sensor and coolant temperature on a cold engine; they should be close, and the reading should change smoothly as the engine warms up.
- Check the sensor's reference voltage and ground at the connector with a multimeter against the manufacturer's specification.
- Check the sensor resistance against the temperature chart for that model, and test the wiring for continuity and shorts to ground or voltage.
- If the wiring and sensor test fine, check the control unit's connector pins and grounds before considering the control unit itself.
How to fix
- Clean, secure or replace a corroded or loose connector, and fix any terminal that is not gripping properly.
- Repair or replace damaged wiring, and secure the harness away from heat and moving parts.
- Replace intake air temperature sensor 2 if its readings are erratic or out of specification.
- Remedy any moisture or oil ingress and fix the source, such as a leaking seal or breather problem.
- Repair faulty grounds or reference supply circuits as found during testing.
- Only if all else is proven sound, repair or replace the engine control unit as advised by the manufacturer.
Can I keep driving?
Low severity
The car can usually be driven for a short time while you arrange a fix, as the control unit will substitute a default air temperature. If it goes into limp mode or runs badly, limit driving and get it checked soon.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.