When the power‑train control module cannot supply the correct voltage to the upstream oxygen‑sensor heater on the first bank, the check‑engine light illuminates and the vehicle’s fuel‑management strategy shifts. Drivers notice a measurable decline in miles‑per‑gallon and, in some cases, a momentary stumble at idle as the engine compensates for an inaccurate oxygen reading. Because the fault is tied to the “positive current control circuit” rather than the sensor’s chemistry, the underlying problem often lies in the module’s output stage or its wiring. Early detection through a diagnostic scan prevents unnecessary component replacement and keeps emissions compliance intact.
These signs appear together or individually, depending on how quickly the module detects the open heater circuit.
The PCM generates a regulated 12‑volt supply to energize the O₂‑sensor heater. Internal MOSFETs or driver transistors can fail due to thermal stress, moisture intrusion, or age‑related solder fatigue. When the driver cannot close, the circuit reads “open,” and the PCM logs P2237.
The heater circuit travels through a dedicated wire bundle from the PCM to the sensor. Chafed insulation, broken pins, or corrosion at connector terminals creates an open condition that the PCM interprets as a control‑circuit fault.
Occasionally, a corrupted flash memory segment or an outdated calibration file mismanages the heater‑control PWM signal. The PCM may incorrectly flag a healthy circuit as open, especially after a failed reflash or incomplete update.
A poor ground path at the PCM or sensor connector can cause the heater voltage to fluctuate, prompting the module to register an intermittent open circuit. Vibration, moisture, or loose bolts are common contributors.
– Connect a OBD‑II scan tool capable of live data and freeze‑frame capture.
– Confirm P2237 and note any accompanying codes (e.g., P0133, P0141) that may indicate secondary sensor issues.
– Visually examine the harness for cracked insulation, burnt spots, or water intrusion.
– Use a multimeter to check continuity from PCM pin 30 (heater‑control output) to sensor pin 2 (heater). Resistance should be ≤ 1 Ω; an open reading confirms a wiring break.
– With the ignition on and the engine at idle, back‑probe the PCM heater‑control pin. A stable 12 V indicates the driver is functional.
– If voltage is absent or erratic, the PCM’s internal driver is suspect.
– Run the scan tool’s “module self‑test” or “communication check” routine. Failure to communicate reliably suggests a deeper PCM fault or a compromised CAN‑bus line.
– Access the manufacturer’s technical service bulletins (TSBs) for the latest PCM calibration. Apply any required reflash using a dealer‑level programmer.
– When voltage is absent and wiring is intact, the PCM must be replaced or re‑programmed.
– Replacement units are matched to the vehicle’s VIN and calibrated to the correct software version before shipping.
– After installation, clear the code, perform a drive cycle, and verify that the readiness monitors set correctly.
– Re‑scan for pending codes.
– Monitor live O₂‑sensor heater voltage and ensure it remains within spec for at least five minutes of operation.
Typical costs
Service Recommendation: Most issues related to this fault are diagnosed and corrected through inspection, wiring repair, and calibration rather than module replacement. For modules not typically replaced through aftermarket suppliers, diagnosis and repair should be performed by a certified automotive technician with access to factory service information and tooling.