P0099: Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic (Meaning, Causes, Fixes)
What P0099 means
An intake air temperature (IAT) sensor is usually a two-wire thermistor. The engine computer (PCM) supplies a reference voltage (normally 5 volts) and a ground, and the sensor's resistance changes with air temperature, which the PCM reads as voltage changes. OBD-Codes.com says P0099 is stored when the PCM detects a certain number of intermittent signals from the #2 IAT sensor over a set period of time. RepairPal describes sensor 2 as the one diesel engines use to measure air going into the charge air cooler (intercooler), and says the code sets when the PCM decides the reading is not plausible. Where sensor 2 sits depends on the vehicle, so check a service manual for yours. P0099 is a generic OBD2 code.
Severity: can I keep driving?
Stop and fix promptly
The sources disagree here. OBD-Codes.com says P0099 should be treated as severe, because the engine computer uses the intake air temperature signal to work out fuel delivery. RepairPal rates it moderate: it may not threaten the vehicle's safety right away, but should be diagnosed within a reasonable time. If the engine hesitates, surges or runs poorly, have it checked soon rather than putting it off.
Common symptoms
- Check engine light on
- Decreased engine performance, especially on a cold start (both sources; cold-start detail from OBD-Codes.com)
- Slightly or noticeably higher fuel consumption (both sources)
- Hesitation or surge at idle or on light acceleration (OBD-Codes.com)
- Other drivability codes may be stored (OBD-Codes.com)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Sensor 2 connector left unplugged after air filter service, which OBD-Codes.com calls by far the most common cause
- Open or shorted sensor 2 wiring or connectors, including corrosion at the connector (OBD-Codes.com; RepairPal lists wiring issue)
- Failed intake air temperature sensor 2 (both sources)
- Faulty mass airflow (MAF) sensor (OBD-Codes.com)
- Clogged air filter or broken intake air inlet pipe (OBD-Codes.com)
- Engine computer (PCM) failure or a PCM programming error, less likely (both sources)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- If the air filter was recently changed, first make sure the intake air temperature sensor connector was plugged back in (OBD-Codes.com).
- Look over the sensor wiring and connector for corrosion, damage or loose pins, and check the air filter and air inlet pipe.
- Check for technical service bulletins for your vehicle.
- Clear the code and test drive. If it comes straight back, keep diagnosing; if it only returns now and then, wiggle-test the wiring with a scan tool watching the sensor 2 reading.
- With a scan tool and an infrared thermometer, compare the IAT 2 reading to the actual intake air temperature (OBD-Codes.com).
Typical fixes
- Reconnect an unplugged sensor connector (OBD-Codes.com)
- Repair open, shorted or corroded wiring and connectors (both sources)
- Replace intake air temperature sensor 2 if it fails resistance or voltage tests (both sources)
- Fix a clogged air filter, broken inlet pipe or faulty MAF sensor if found (OBD-Codes.com)
- Suspect the PCM or its programming only after the sensor and circuits check out (both sources)
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- Resistance test of the sensor against the manufacturer's specification with a digital volt-ohm meter (OBD-Codes.com)
- Checking for the reference voltage and ground, then comparing sensor output voltage to the manufacturer's voltage-to-temperature chart (OBD-Codes.com)
- With the related controllers unplugged, testing resistance and continuity on all system circuits (OBD-Codes.com)
- PCM testing, replacement or reprogramming
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Can I keep driving with P0099?
The sources disagree. OBD-Codes.com says to treat it as severe because the signal feeds fuel delivery, while RepairPal rates it moderate. If the engine hesitates or surges, get it checked soon, and start by making sure the sensor is plugged in.
How is P0099 different from P0097 and P0098?
All are for intake air temperature sensor 2. P0097 is a signal stuck low (reads very hot air) and P0098 a signal stuck high (reads very cold air). P0099 means the signal is cutting in and out or jumping around, which usually points to a loose connector or intermittent wiring fault. P0095 is the general circuit code and P0096 range/performance.
Why did P0099 show up right after an oil change or air filter change?
OBD-Codes.com says the most common cause is a sensor connector left unplugged when the air filter was checked or replaced. Check that first.
Do the sources agree on the details?
Partly. Both name the sensor, wiring and, less often, the PCM, and both list reduced performance and higher fuel use. They differ on severity: OBD-Codes.com says severe, RepairPal says moderate. They also describe the trigger differently: OBD-Codes.com says the PCM counted too many intermittent signals in a set time, while RepairPal says the PCM found the reading not plausible. RepairPal frames sensor 2 as a diesel charge air cooler sensor, while OBD-Codes.com treats P0099 as a generic code and also lists a faulty MAF sensor, a clogged air filter and a broken inlet pipe as causes, which RepairPal does not mention.
Sources
Last reviewed 2026-10-24. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.