What Does Fault Code P0112 Mean?
Fault code P0112 is a generic OBD-II diagnostic trouble code defined as “Intake Air Temperature Sensor 1 Circuit Low Input” . This indicates that the vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the voltage signal from the Intake Air Temperature (IAT) Sensor 1 is lower than the expected normal operating range, typically indicating a short circuit to ground in the sensor circuit .
Background: The Intake Air Temperature (IAT) sensor is a thermistor (a temperature-sensitive resistor) that measures the temperature of the air entering the engine’s intake manifold . The ECM/PCM supplies it with a 5-volt reference signal. As air temperature increases, the sensor’s resistance decreases, causing the signal voltage to drop. Code P0112 is set when the ECM detects the signal voltage is persistently too low, often below a specific threshold like 0.18 volts for more than 0.5 seconds, which corresponds to an implausibly high temperature reading (often around 140°C or 284°F) . When this happens, the ECM typically enters a fail-safe mode and uses a default temperature value (often 16°C or 60.8°F) for fuel calculations, which can affect performance and emissions .
Symptoms of Fault Code P0112
- Illuminated Check Engine Light (MIL) .
- Poor fuel economy (decreased MPG) due to incorrect air-fuel mixture calculations .
- Rough engine idle or potential stalling .
- Engine hesitation, stumbling, or lack of power during acceleration .
- Black smoke from the exhaust during acceleration, indicating a rich fuel mixture .
- Engine may be hard to start, especially when warm .
Main Causes of Fault Code P0112
- Short Circuit to Ground: The most common cause is the IAT sensor signal wire being shorted (touching) to a ground point or the sensor’s ground wire, causing the voltage to drop to near zero .
- Faulty IAT Sensor: The sensor itself has failed internally, providing an incorrect low-resistance (high-temperature) signal .
- Damaged Wiring or Connectors: Corroded, frayed, or damaged wires and connectors in the IAT sensor circuit can create a path to ground .
- Poor Electrical Connection: Loose, corroded, or damaged pins at the sensor or ECM connector can cause a poor connection that mimics a short .
- Faulty Engine Control Module (ECM/PCM): A rare cause where the control module itself has an internal fault, incorrectly interpreting a normal sensor signal as low .
How to Diagnose Fault Code P0112?
- Scan and Record: Connect an obd2 scanner to confirm code P0112 and check for any related codes (e.g., P0111, P0113). Record freeze frame data to see the engine conditions when the fault occurred .
- Monitor Live Data: Using a capable scanner, monitor the live IAT sensor reading. A reading stuck at an implausibly high value (e.g., 121°C / 250°F or 140°C / 284°F) strongly indicates a short circuit .
- Visual Inspection: Inspect the IAT sensor (often integrated into the Mass Air Flow sensor assembly), its wiring harness, and connectors for obvious damage, chafing, or corrosion that could cause a short to ground .
- Test the Sensor and Circuit: With the ignition OFF, disconnect the IAT sensor connector. Using a digital multimeter, check for continuity (resistance near 0 ohms) between the sensor signal wire terminal and chassis ground. If continuity exists with the sensor disconnected, the wiring harness is shorted to ground .
- Sensor Test: Measure the resistance of the disconnected IAT sensor itself across its terminals. Compare the reading at ambient temperature to the manufacturer’s specifications. An unusually low resistance may indicate a faulty sensor .
Possible Causes and Diagnostic Methods
Possible Cause | How to Check? |
|---|---|
Short Circuit to Ground (Wiring) | With the sensor disconnected, use a multimeter to check for continuity between the signal wire pin in the harness connector and chassis ground. If continuity exists, the wire is shorted . |
Faulty IAT Sensor | Measure the sensor’s resistance. If it is extremely low (e.g., near 0 ohms) at room temperature, the sensor is likely shorted internally and needs replacement . |
Damaged Wiring/Connector | Perform a thorough visual and physical inspection (wiggle test) of the entire wiring harness from the sensor to the ECM, looking for damaged insulation or corroded terminals . |
Poor Ground Connection | Check the ground circuit for the sensor and ECM for high resistance or corrosion, which can affect the signal . |
Faulty PCM | A last-resort diagnosis. If all wiring tests are normal and a known-good sensor still causes the code, the PCM may be faulty. Check for technical service bulletins (TSBs) first . |
Required Tools: OBD2 code reader, digital multimeter (DMM), basic hand tools, vehicle-specific wiring diagrams.
How to Fix Fault Code P0112? (Solutions)
Simple Fixes:
- Repair Wiring: Locate and repair any section of the IAT signal wire that is shorted to ground. Use solder and heat-shrink tubing for a proper repair.
- Clean/Repair Connectors: Disconnect the IAT sensor and ECM connectors, clean any corrosion from the terminals, and ensure they are tightly connected.
In-Depth Diagnosis and Repair:
- Replace the IAT Sensor: If the sensor itself tests as shorted, replace it. On many vehicles, this is part of the MAF/IAT sensor assembly .
- Replace Wiring Harness Section: If the short is within a damaged section of the harness that cannot be reliably repaired, replace that section.
- Update PCM Software: In rare cases, a software glitch may cause a false code. Check for available PCM updates from the manufacturer.
- Replace PCM: Only after all other possibilities are exhausted and diagnostics point conclusively to an internal PCM fault.
Troubleshooting by Symptom
Symptom | Likely Solution |
|---|---|
Check Engine Light on with black smoke and poor fuel economy. | Likely a shorted IAT sensor or wiring, causing the ECM to think the intake air is extremely hot and enriching the fuel mixture excessively. |
Rough idle and hard starting. | Could be caused by the ECM using a default temperature value that is incorrect for current conditions, leading to poor fuel mixture at startup. |
Code returns immediately after clearing. | Indicates a persistent hard fault, most commonly a permanent short to ground in the wiring or a internally shorted sensor. |
Common Vehicles with Fault Code P0112
- Mitsubishi Vehicles: The factory diagnostic procedure is precise. Code P0112 sets under specific conditions (e.g., engine run time > 3 min, vehicle speed 10s). Diagnosis involves checking the harness between the air flow sensor connector and the engine-ECU connector for shorts to ground .
- Chrysler/Dodge/Jeep Vehicles: The PCM monitors the IAT sensor signal voltage. A “Circuit Low” fault (P0112) is set if the voltage reads below the low calibrated threshold. Common causes are the IAT signal circuit shorted to ground, shorted to the sensor ground, a faulty IAT sensor, or a faulty PCM .
- General Motors (GM) Vehicles (Chevrolet, Buick, GMC, Cadillac): For GM, DTC P0112 sets when the ECM detects the IAT sensor voltage is greater than 4.87 volts for more than 1 second or cumulatively for 10 seconds under specific conditions (engine warm, idling, low airflow) . This indicates a circuit low condition (high voltage corresponds to low temperature signal, but the logic flags it as “low input” relative to expected range).
- Alfa Romeo Vehicles: The diagnostic compares values from the Ambient, Engine Coolant, and Intake Air Temperature sensors after a cold start. If the IAT sensor disagrees with the others, it’s declared irrational. Causes include loose connections at the PCM or sensor, poor wiring insulation, or poor continuity in the sensor or ground wiring .
- Mini Cooper/BMW: Common causes include a faulty IAT sensor (often integrated), wiring issues, or problems with the Engine Control Unit (ECU). Air intake leaks can also affect readings.
- Ford Vehicles: Prone to wiring harness damage due to heat and vibration in the engine bay, leading to shorts.
- Toyota/Lexus: The IAT sensor is often part of the MAF assembly. Wiring connector issues are frequent. The ECM uses a default value of 16°C when the code is set .
- Honda/Acura: Similar to others, causes include sensor failure and wiring shorts. Diagnosis involves checking sensor resistance and circuit continuity.
- Nissan/Infiniti: Known for connector corrosion and sensor failures, especially in older models.
- Volkswagen/Audi: The IAT sensor is typically integrated. Faults often stem from wiring shorts or internal sensor failures.
P0112 Frequently Asked Questions
What does the P0112 code specifically mean?
It means the vehicle’s computer has detected that the signal voltage from the Intake Air Temperature (IAT) Sensor 1 is too low, which usually corresponds to the sensor reporting an implausibly high air temperature (often around 140°C/284°F). This indicates a short to ground in the circuit or a failed sensor .What is the difference between P0112, P0111, and P0113?
- P0112: “Circuit Low Input” – The sensor signal voltage is too low (short to ground), making the ECM think the air is extremely hot.
- P0111: “Circuit Range/Performance” – The sensor signal is within range but erratic or not changing logically.
- P0113: “Circuit High Input” – The sensor signal voltage is too high (open circuit), making the ECM think the air is extremely cold (~ -40°C/-40°F) .
Is it safe to drive with a P0112 code?
You can usually drive for a short time, but it is not recommended. The engine will be in a fail-safe mode, which can cause poor fuel economy, reduced performance, rough running, and increased emissions. Prolonged driving may lead to carbon buildup or other issues .Can I fix a P0112 code myself?
Yes, if you have basic mechanical and electrical skills. Start by using a car scanner to confirm the code and view live data. Then, visually inspect the sensor and wiring for obvious damage. Checking for a short circuit with a multimeter is a key diagnostic step .Why does my P0112 code keep coming back after I clear it?
This indicates a persistent “hard” fault. The most common reason is a permanent short to ground in the wiring harness or a completely failed (shorted) IAT sensor. The fault is immediately redetected once the system runs its self-check.How much does it cost to fix a P0112 code?
Costs vary: The IAT sensor itself typically costs between 100. Professional diagnosis and repair at a shop can range from 300, depending on labor rates and whether it’s a simple sensor replacement or requires wiring repair .Do I need to replace the entire MAF sensor for a P0112 code?
Often, yes. On most modern vehicles, the IAT sensor is built into the Mass Air Flow (MAF) sensor assembly as a single, non-serviceable unit. If the IAT portion is faulty, the entire MAF/IAT unit must be replaced.What should the IAT sensor read on a scan tool with a P0112 code?
With a P0112 code present, the live data from the IAT sensor will typically be stuck at an implausibly high value, such as 121°C (250°F) or 140°C (284°F), regardless of the actual air temperature .How do I test an IAT sensor for a P0112 code?
Disconnect the sensor. Measure its resistance with a multimeter. At room temperature (around 20°C/68°F), a typical IAT sensor resistance might be 2000-3000 ohms. If you measure a resistance near 0 ohms, the sensor is internally shorted and faulty .Will disconnecting the battery clear P0112 permanently?
No. It will clear the code and turn off the light temporarily, but the ECM’s self-tests will run again. If the short circuit or faulty sensor is still present, the code will return, usually within one or two drive cycles.Can a dirty air filter cause P0112?
No, a dirty air filter cannot directly cause a P0112 code. P0112 is an electrical circuit fault (low voltage/short), not a performance issue caused by airflow restriction.
Related OBD2 Fault Codes
- P0110 – Intake Air Temperature Sensor 1 Circuit Malfunction
- P0111 – Intake Air Temperature Sensor 1 Circuit Range/Performance Problem
- P0113 – Intake Air Temperature Sensor 1 Circuit High Input
- P0114 – Intake Air Temperature Sensor 1 Circuit Intermittent
Important Note!Code P0112 indicates a specific electrical fault: a short to ground. The most effective diagnostic step is to use a vehicle diagnostics tool to view live data and see the implausibly high temperature reading, then use a multimeter to test for a short in the wiring with the sensor disconnected. Never ignore this code, as it forces the engine to run in a fail-safe mode that can harm performance and efficiency. For complex wiring issues, consulting vehicle-specific repair information or a professional technician is advised.