Safe to drive in most conditions. Repair within a few weeks. P0113 means the intake air temperature (IAT) sensor circuit is reporting a voltage above its valid operating range, which the ECM interprets as an open circuit — typically corresponding to an indicated temperature well below the actual ambient reading.
What P0113 means
The IAT sensor is a thermistor integrated into the MAF sensor assembly on most modern engines. It works as a variable resistor: as intake air temperature rises, the sensor resistance decreases and the voltage at the ECM input terminal falls. The ECM supplies a 5V reference through a series resistor; the resulting voltage drop across the sensor is what the ECM reads. P0113 fires when that input voltage stays above approximately 4.91 V for 0.5 seconds or longer with the ignition on — a reading the ECM associates with a temperature below −55°C (−67°F) that is physically impossible under normal operating conditions. In practice this signals an open circuit: either the IAT sensor has failed internally, the wiring between the sensor and ECM has broken, or the connector has lost contact. When P0113 is stored, the ECM enters a fail-safe mode and substitutes a fixed IAT value (typically 20°C / 68°F) for fuel calculation purposes.
Symptoms
- Check engine light on
- IAT temperature reading displayed as −40°C (−40°F) or a similarly impossible negative value on a scan tool
- Possible rich fuel mixture at cold start — the ECM's substituted temperature may cause over-fuelling in very cold ambient conditions
- Possible black smoke or a briefly rough start in freezing weather if the ECM's assumed IAT significantly underestimates actual intake temperature
- No noticeable drivability symptoms in most warm-weather conditions due to fail-safe substitution
Common causes
- Open circuit in the IAT sensor signal wire between the sensor and the ECM — the most common cause
- Corroded or damaged connector at the MAF/IAT sensor harness plug breaking the signal path
- Failed IAT sensor thermistor element with an internal open — the sensor's resistance has gone to infinity
- Damaged wiring harness routing near heat sources or sharp brackets causing an intermittent wire break
- Faulty ECM input circuit — rare but possible if the 5V reference or signal input has failed internally
Severity & driving advice
Severity: Low — Fail-safe substitution masks the fault in normal operation. Extreme cold may cause brief start roughness. Repair soon to restore accurate fuelling.
Can I drive? Safe to drive in most conditions. Repair within a few weeks.
Diagnostic approach
- Read the live IAT value on a scan tool — With the ignition on (engine off is fine), check the IAT reading. P0113 typically displays as −40°C / −40°F, which is the sensor's zero-voltage floor value — not a real temperature. If the reading is −40 and the ambient temperature is clearly much warmer, an open circuit in the sensor or wiring is confirmed.
- Inspect the MAF/IAT sensor connector for damage — Unplug the sensor harness connector and examine the terminals for corrosion (green or white oxidation), bent pins, or pushed-back terminals. Spread any collapsed female terminals with a small pick. Reconnect firmly and clear the code. A large proportion of P0113 faults on high-mileage vehicles are caused by connector corrosion rather than a failed sensor.
- Measure IAT sensor resistance with a multimeter — Disconnect the sensor connector and measure resistance across the two IAT signal terminals on the sensor side. At typical ambient temperature (20°C / 68°F) the IAT thermistor should read approximately 2,000–3,000 ohms. An open-circuit (infinite resistance) reading confirms the sensor has failed internally. Check the sensor's temperature-resistance curve in the service data for the specific specification at your measured ambient temperature.
- Check wiring continuity to the ECM — If the sensor tests good (resistance in range), trace the signal wire from the sensor connector to the ECM. Probe continuity with a multimeter between the sensor signal terminal and the corresponding ECM pin. No continuity (open) means a broken wire in the harness — inspect for chafing near hot surfaces, zip tie wear points, or rodent damage.
Typical repair costs
| Component | Low estimate | High estimate |
|---|---|---|
| MAF/IAT sensor replacement (combined unit) | $80 | $280 |
| Wiring harness repair (open circuit) | $50 | $200 |
| Connector / terminal repair kit | $15 | $60 |
Make & model notes
Toyota: On Toyota engines where the IAT sensor shares the MAF housing (virtually all post-2000 models), P0113 nearly always means the combined MAF/IAT sensor unit needs replacement. The IAT thermistor inside cannot be serviced independently from the MAF element, and attempting to repair it risks disturbing the sensitive hot-wire film. Confirm with a resistance test first — corrosion at the connector resolves more cheaply.
Ford: Ford vehicles with separate stand-alone IAT sensors mounted in the intake manifold or air duct (older Mustang, Explorer, early F-150) allow the IAT sensor to be replaced independently for under $30. Check whether your specific Ford application has a standalone IAT or a combined MAF/IAT unit before ordering parts.
Honda: Honda Civic and Accord applications with the IAT sensor integrated into the MAF develop P0113 primarily from connector corrosion at the multi-pin harness plug rather than sensor failure. The connectors on these engines are exposed in the engine bay and corrode at the brass terminals over time. Terminal cleaning or replacement with an aftermarket pigtail connector frequently resolves P0113 without purchasing a new MAF/IAT sensor.
FAQ
Why does P0113 show −40°C on the scan tool?
−40°C (which equals −40°F) is the ECM's minimum-scale value for the IAT input — it corresponds to maximum voltage (approximately 5V) at the sensor input terminal. When the circuit is open (broken wire or failed sensor), the input sees full reference voltage with no sensor pulling it down, so the ECM reads it as the coldest possible temperature.
Can P0113 affect fuel economy?
In most conditions, no. The ECM's fail-safe substitutes a moderate ambient temperature (around 20°C / 68°F) which is close enough to real-world conditions to maintain reasonable fuelling. In very cold weather (below −10°C), the substituted value would be warmer than reality, causing the ECM to command slightly less cold-start enrichment than needed — this can cause a briefly rough start.
Is the IAT sensor the same part as the MAF sensor?
On most modern vehicles, yes — the IAT thermistor is integrated into the MAF sensor housing. Replacing the MAF sensor also replaces the IAT sensor in these applications. Some older vehicles have a separate IAT sensor mounted in the intake manifold or ducting, which can be replaced independently at low cost.
Can I drive indefinitely with P0113?
In temperate climates, the fail-safe value is close enough to actual conditions that you will not notice a problem. However, the fail-safe prevents proper cold-start enrichment calibration in extreme cold, and the underlying open circuit may also affect MAF sensor wiring on shared harnesses. Repair within a few weeks to restore full system function.