P1117 IAT Sensor Intermittent Low Voltage
The P1117 code indicates an intermittent low voltage condition in the intake air temperature (IAT) sensor circuit. The engine control module (ECM) detects that the IAT sensor signal voltage sporadically drops below the expected operating range. This typically occurs when circuit resistance momentarily decreases, causing the ECM to interpret an unusually high air temperature. The IAT sensor is a thermistor whose resistance varies with temperature; a low signal voltage tells the ECM the air is very hot. Because the fault is intermittent, it may not be present continuously, making diagnosis challenging. Common underlying issues include loose connections, vibration-induced faults, or moisture in the connectors.
01. Most Common Causes
- Loose or dirty connection in the IAT sensor harness
- Intermittent short-to-ground in the wiring
- Faulty IAT sensor with internal thermal failure
- Corrosion on the sensor connector terminals
- Intermittent 5V reference supply issue from the ECM
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Possible poor fuel economy or rough idle
03. Step-by-Step Diagnosis
Scan for codes and verify P1117 is present along with any related codes.
Visually inspect the IAT sensor connector and wiring for damage, corrosion, or loose fit.
Monitor IAT sensor voltage with a scan tool while gently wiggling the harness to reproduce the intermittent fault.
Check for a short to ground by measuring resistance between the signal wire and ground with the sensor disconnected.
If no wiring issues found, test the IAT sensor resistance at known temperatures and compare to specifications.
1. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive short distances, but the engine may run rich, reducing fuel economy and potentially causing long-term damage to the catalytic converter. Have it diagnosed soon.
How much does it cost to fix?▼
Repair costs typically range from $50 to $200, depending on whether it's a simple connector cleaning or sensor replacement. Diagnostic fees may add $50–$100.