Drivers first notice the check‑engine lamp come on, often accompanied by a subtle drop in fuel economy or a rougher idle. Some owners report a momentary hesitation when the throttle is opened, especially at low speeds. In severe cases the engine may run unevenly long enough for the PCM to flag a diagnostic trouble code. Because the code specifically references “O₂ Sensor Positive Current Control Circuit Low Bank 1 Sensor 1,” the underlying problem is a low‑voltage condition in the circuit that supplies the upstream oxygen sensor on the side of the engine containing cylinder 1.
The PCM/ECU contains a driver that supplies a regulated 5 V reference to the upstream O₂ sensor. Internal failure of this driver—often due to moisture intrusion or component fatigue—produces a low‑voltage reading that triggers P2238.
A short to ground, broken conductor, or corrosion at the sensor connector can drop the voltage below the sensor’s minimum threshold. Even a single compromised pin in the harness can cause the circuit to read low.
Oxidation or loose pins at the sensor plug or PCM connector interrupt the positive current path. Intermittent contact may explain occasional hesitation and a fluctuating idle.
Out‑of‑date PCM firmware or a corrupted flash map can misinterpret the sensor’s voltage signal, flagging a low‑current condition when the hardware is functional.
While the sensor itself can fail, a sensor that draws excessive current can also pull the voltage down. In many cases the sensor’s internal heater circuit is the culprit, but the primary diagnostic focus should remain on the control circuit that the PCM governs.
Use a professional scan tool to read live data while the engine is at idle and under light load. Verify the O₂ sensor voltage (Bank 1 Sensor 1). A reading consistently below 0.2 V indicates a low‑current condition.
With the ignition on and the engine off, measure the voltage at the sensor’s positive supply pin. Expect ~5 V. If the voltage is low, trace back to the PCM connector.
Visually examine the harness for chafing, broken wires, or water intrusion. Disconnect the sensor plug, clean the contacts with an appropriate electrical cleaner, and re‑seat the connector. Check for continuity and resistance; any reading above 2 Ω suggests a compromised conductor.
Some advanced scan tools can command the PCM to output a test voltage on the sensor circuit. Compare the commanded voltage to the actual reading at the sensor. A discrepancy points to a module‑level fault.
If the hardware checks out, download the latest PCM calibration from the manufacturer’s service portal and flash the module. Re‑run the test to confirm the voltage now meets spec.
Should the driver remain out of spec after cleaning and software update, the PCM’s internal current‑drive circuitry is likely damaged. A re‑programming attempt may restore proper operation, but many technicians opt for a replacement module that is VIN‑matched and pre‑programmed.
After repair, clear the DTC and conduct a drive cycle of at least 10 minutes under varied load. Confirm that P2238 does not reappear and that fuel‑trim values return to normal ranges (typically 0 % ± 5 %).
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.