P1118 — IAT Sensor Open/Short

OBD2 code P1118 flags a problem with the sensor and actuator circuits (IAT sensor open/short). The car is usually drivable while you plan the repair. Common culprits: blown fuse feeding the circuit, poor ground connection, corroded, loose or damaged connector.

For Ford vehicles

manifold air temperature circuit – signal too low

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P1118 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the IAT sensor open/short for damage, corrosion, chafing or poor contact.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P1118 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P1118 (parts and labor, USD, independent shop rates): Replace the faulty sensor or actuator: $150–$500; Control module repair: $300–$1,000; Repair wiring or connectors: $80–$250. Overall, fixing P1118 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How do I diagnose P1118 myself?

Start with a scan: confirm P1118, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the sensor and actuator circuits, and verify the suspect component against live data before buying parts.

What does OBD2 code P1118 mean?

Will P1118 clear itself?

Sometimes P1118 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

Is it safe to drive with P1118?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

What are the symptoms of P1118?

Drivers most often notice: possible limp mode depending on the affected component, the affected system operates intermittently or not at all, increased fuel consumption in some cases, Check Engine Light on.

The engine control module logs code P1118 when it detects an electrical fault in the Intake Air Temperature sensor circuit. The IAT sensor measures the temperature of incoming air and sends that data to the ECU, which uses it to calculate fuel delivery and ignition timing. When the circuit goes open or shorts out, the module can no longer receive a usable signal. The ECU does not trigger P1118 based on a single bad reading; it requires the fault condition to appear repeatedly under specific operating conditions before it activates the Check Engine light. This is a safety mechanism to prevent false alarms from temporary electrical glitches.

When P1118 sets, the stored freeze frame data captures exactly what was happening at the moment the fault occurred — engine load, RPM, coolant temperature, and vehicle speed. That snapshot is valuable during diagnosis because it tells you which conditions to replicate when testing. You can use that data to confirm whether the problem happens during cold starts, high loads, or specific speeds. Without reproducing those conditions, you may test the sensor when it works correctly and miss the intermittent fault.

Common Symptoms of P1118

The Check Engine light illuminates on the dashboard
The engine may enter a reduced-power or limp-home mode depending on which component is affected
The affected circuit or system operates intermittently or stops working entirely
Fuel economy drops noticeably in some vehicles
The engine may run roughly or show poor throttle response

What Causes P1118?

A corroded, loose, or physically damaged connector at the IAT sensor or related component
An open circuit or shorted wire somewhere in the wiring harness for the affected sensor or actuator
The sensor or actuator itself has failed internally
A poor or interrupted ground connection for the circuit
A driver fault inside the engine control module
A blown fuse that supplies power to the affected circuit

How to Diagnose P1118

Plug in an OBD2 scanner and confirm that P1118 is stored in the ECU memory. Save the freeze frame data immediately — this record shows the engine conditions when the fault was detected.
Look for any other stored trouble codes. Related codes often point to the actual root cause or a second problem in the same circuit. Check manufacturer technical service bulletins for your specific make and model — some P0xxx codes have known factory fixes or software updates listed by VIN on the manufacturer or NHTSA websites.
Perform a hands-on visual inspection of the wiring harness and connectors tied to the IAT circuit. Look for broken insulation, chafing from rubbing against brackets, corrosion on the terminals, or connectors that are not fully seated.
With the connector unplugged, measure reference voltage, ground integrity, and signal continuity at the component harness using a multimeter. Compare your readings to the manufacturer's specifications.
While monitoring live data on the scanner, gently wiggle the harness and connector. Any dropouts or signal interruptions indicate a broken wire or loose terminal inside the insulation.
Clear P1118 from memory, then drive the vehicle through a complete drive cycle that includes the conditions recorded in the freeze frame. If the code does not return, the fault was likely temporary. If it returns, you have confirmed an active problem that requires repair.

Repair Options for P1118

Begin with the least expensive and most frequently encountered repairs before committing to costly component replacements:

Replace the faulty sensor or actuator — parts and labor typically run $150–$500
Repair wiring or connectors — parts and labor typically run $80–$250
Control module diagnosis and repair — parts and labor typically run $300–$1,000

How Much Does It Cost to Fix P1118?

The total bill depends entirely on which part is actually at fault. Here are typical scenarios for P1118 at independent shop rates in USD:

Sensor or actuator replacement: $150–$500
Wiring harness or connector repair: $80–$250
Engine control module repair or replacement: $300–$1,000

Most drivers can expect to spend somewhere between $80 and $1,000 to resolve P1118. Getting an accurate diagnosis before purchasing parts is the single most effective way to control costs — the most expensive scenario is rarely the first thing you should check.

Driving Safety Verdict

P1118 carries a short-term severity rating. In most cases the vehicle remains drivable, though you may notice slightly reduced performance or a disabled auxiliary system. If the car develops stalling, a hard no-start condition, or warnings affecting the brakes or steering, treat the situation as urgent and stop driving immediately. Otherwise, schedule the repair within a few days to prevent the fault from worsening or triggering cascading issues in related systems.