What Does P1115 Mean?
P1115 indicates the Engine Coolant Temperature (ECT) sensor circuit is producing an intermittent high voltage signal, or the secondary IAT-B circuit has a high input. An intermittent high voltage on the ECT makes the ECM believe the engine is colder than it actually is, causing excessive fuel enrichment, elevated idle speed, and possible catalytic converter damage from over-rich exhaust. Electric cooling fans may not engage when needed.
Common Causes
30%
Intermittent open circuit in the ECT sensor signal or ground wire
25%
ECT sensor connector loose or making poor contact
20%
ECT sensor developing intermittent high resistance internally
15%
IAT-B sensor (secondary intake) circuit open intermittently
10%
ECM connector pin backed out or corroded at the ECT input
Diagnostic Steps
1
Step 1: Monitor ECT sensor live data during warm-up. If the reading intermittently drops to -40°F or stays unrealistically cold, the circuit is going open intermittently, producing high voltage.
2
Step 2: Wiggle the ECT sensor connector and harness while monitoring the PID. An intermittent open will show as a sudden jump to a very cold reading.
3
Step 3: Disconnect the ECT sensor and check resistance. It should be proportional to actual engine temperature — approximately 2,000–3,000 ohms cold, 200–300 ohms warm. Erratic or infinite readings confirm failure.
4
Step 4: Verify continuity and resistance of the signal and ground wires from the ECT connector back to the ECM. Check for any splice points or junction connectors that may have corrosion.
5
Step 5: Replace the ECT sensor if resistance testing is intermittent or out of range. Also check the thermostat housing seal where the sensor threads in for coolant seepage that may corrode the connector.
Estimated Repair Cost
$30 - $200
Parts + labor, varies by vehicle and location
P1115 indicates the Engine Coolant Temperature (ECT) sensor circuit is producing an intermittent high voltage signal, or the secondary IAT-B circuit has a high input. An intermittent high voltage on the ECT makes the ECM believe the engine is colder than it actually is, causing excessive fuel enrich...
The most common cause of P1115 (Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage/IAT - B Circuit High Input) is: Intermittent open circuit in the ECT sensor signal or ground wire
Typical repair costs for P1115 range from $30 to $200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An ECT circuit reading falsely cold can prevent cooling fan activation, causing engine overheating that may lead to head gasket failure or engine damage. Rich running can also overheat catalytic converters.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1115 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Management / Cooling System Monitoring
Difficulty
Type
Manufacturer
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