Evaporative Emission System Leak Detection Pump Heater Control Circuit Low
Diagnostic trouble code P240B indicates that the powertrain control module (PCM) has detected a low voltage condition in the control circuit for the evaporative emission (EVAP) system leak detection pump heater. This typically means the circuit is shorted to ground or has excessive resistance, preventing the heater from operating correctly to prevent condensation or freezing within the pump.
This code does not affect the drivability or safety of the vehicle. However, it will cause the check engine light to illuminate and may prevent the vehicle from passing an emissions test.
Common symptoms
- Illuminated Check Engine Light (MIL)
- Failure to pass an emissions inspection
- Possible secondary EVAP system codes due to frozen or malfunctioning leak detection pump in cold weather
- No noticeable drivability issues
- Slight decrease in fuel economy (rare)
Likely causes
- Faulty EVAP leak detection pump heater (internal failure)
- Wiring harness shorted to ground in the heater control circuit
- Corroded, damaged, or loose electrical connector at the leak detection pump
- Blown fuse for the EVAP heater circuit (often caused by a short)
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Check the fuse for the EVAP leak detection pump heater circuit.
Look for: A blown fuse indicates a short circuit in the wiring or inside the heater element itself.
Visually inspect the wiring harness and connector at the EVAP leak detection pump.
Look for: Look for chafed wires, bare copper touching the chassis (short to ground), or green corrosion inside the connector pins.
Measure the resistance of the leak detection pump heater element using a multimeter.
Look for: Compare the resistance reading to the manufacturer's specification. An extremely low reading indicates an internal short, while an infinite reading (OL) indicates an open circuit.
Check for voltage at the heater connector with the key on (or when commanded by a scan tool).
Look for: If there is no voltage present, the issue lies upstream in the wiring, a relay, or the PCM.
Test the ground circuit for the heater at the connector.
Look for: A high resistance reading to battery ground indicates a poor ground connection, which can affect circuit operation.
This page explains the generic P240B definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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