The OBD2 code P0099: Intake Air Temperature Sensor 2 Circuit Intermittent signals intermittent readings from the vehicle’s second intake air temperature sensor. This sensor’s data is crucial for the engine control module (ECM) to adjust fuel injection and ignition timing accurately. Fluctuations in the sensor’s output can cause the engine to run inefficiently, leading to symptoms like rough running or a persistent check engine light.
P0099 quick overview
| Meaning | P0099: Intake Air Temperature Sensor 2 Circuit Intermittent |
| Is it serious? | Yes, it can lead to engine performance issues and should be addressed to maintain optimal operation. |
| Possible causes | – Faulty IAT sensor – Damaged or loose wiring or connectors – ECM software issues |
| How to diagnose? | Check MAF sensor connector and wiring for issues. Test IAT sensor 2 circuit for continuity and voltage drop. Verify ECM ground circuits for proper function. Inspect multifunction intake air sensor terminals for corrosion. Consider PCM reflash if a software issue is suspected. |
P0099 Meaning
Imagine your car’s engine as a person trying to breathe through a straw while running. The IAT sensor helps adjust the straw’s size to make breathing easier or harder based on how hot or cold the air is. When the P0099 code pops up, it’s like the sensor starts randomly changing the straw’s size, making the engine work harder than it needs to. Fixing this helps your car “breathe” just right again, smoothing out those engine hiccups.
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How to fix P0099 – learn from mechanics
I looked into P0099 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Chevrolet P0099
Vehicle Information 2012 Chevrolet Camaro LS 3.6L
Issue + Repair History
- MIL light on with running rough symptoms.
- Previous codes: random misfire, evap code, P0099, P114c.
- Spark plugs and ignition coil for cylinder 5 replaced.
- Evap purge solenoid replaced.
- New GM MAF sensor installed.
- MIL light persists despite repairs.
Other OBD2 Codes + Test Results
- OBD2 Codes: P0099 (Intake air temperature sensor 2 circuit intermittent), P114c (Intake air humidity sensor erratic performance).
- IAT sensor 1 and IAT sensor 2 readings differ by approximately 18 degrees.
- MAF sensor disconnected results in both IAT sensor readings dropping to -40°C.
Mechanic Suggestions
- Check MAF sensor connector and wiring for any issues.
- Test IAT sensor 2 circuit for continuity and voltage drop.
- Verify proper function of ECM ground circuits.
- Inspect multifunction intake air sensor terminals for corrosion.
- Consider the possibility of a software issue requiring PCM reflash.
Final Fix After installing a new GM MAF sensor and confirming proper wiring connections, the MIL light remained off for two days before reappearing. Further investigation revealed that the vehicle owner had installed aftermarket ECM programming, causing performance issues. Due to the complexity of the programming issue, it was recommended to seek assistance from a dealer for resolution.
Case #2: Ford P0099
Vehicle Information 2010 Ford Fusion SE 2.5L
Issue + Repair History
- Check engine light on.
- Previous repairs: none mentioned.
Other OBD2 Codes + Test Results
- OBD2 Code: P0099 (Intake air temperature sensor 2 circuit intermittent).
- No additional codes reported.
- Live data shows inconsistent readings from IAT sensor 2.
Mechanic Suggestions
- Inspect IAT sensor 2 and its wiring for damage or corrosion.
- Check connector integrity at the IAT sensor 2 and ECM.
- Test IAT sensor 2 circuit for shorts to ground or power.
- Consider replacing the IAT sensor 2 if no other issues are found.
Final Fix After thorough inspection of the IAT sensor 2 circuit and wiring, it was discovered that the sensor connector had a loose pin causing intermittent signal interruption. Replacing the connector and ensuring proper connection resolved the issue, and the vehicle no longer displayed the P0099 trouble code.
Case #3: Toyota P0099
Vehicle Information 2015 Toyota Corolla LE 1.8L
Issue + Repair History
- Check engine light on.
- Previous repairs: none mentioned.
Other OBD2 Codes + Test Results
- OBD2 Code: P0099 (Intake air temperature sensor 2 circuit intermittent).
- No additional codes reported.
- Live data shows inconsistent readings from IAT sensor 2.
Mechanic Suggestions
- Inspect IAT sensor 2 and its wiring for damage or corrosion.
- Check connector integrity at the IAT sensor 2 and ECM.
- Test IAT sensor 2 circuit for shorts to ground or power.
- Consider replacing the IAT sensor 2 if no other issues are found.
Final Fix Upon investigation, it was found that the wiring harness near the IAT sensor 2 had been damaged due to rodent activity, causing intermittent connectivity issues. Repairs were made to the wiring harness, and the IAT sensor 2 was replaced as a precautionary measure. After repairs, the vehicle’s check engine light remained off, and no further occurrences of the P0099 trouble code were observed.
How to diagnose P0099
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Brief Explanation |
|---|---|
| Check MAF sensor connector and wiring | Identifies potential issues affecting sensor readings. |
| Test IAT sensor 2 circuit | Finds breaks or shorts that could cause intermittent signals. |
| Verify ECM ground circuits | Ensures the ECM has a good ground, critical for accurate sensor operation. |
| Inspect intake air sensor terminals | Looks for corrosion that might interrupt sensor signals. |
| Consider PCM reflash | Addresses possible software glitches affecting sensor data interpretation. |
Car Diagnostics Training
- Car Electrical basics
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I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko