P2238
O2 Sensor Positive Current Control Circuit Low, Bank 1 Sensor 1P2238 is a generic OBD-II powertrain diagnostic trouble code: O2 Sensor Positive Current Control Circuit Low, Bank 1 Sensor 1. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P2238 means
Code P2238 applies exclusively to vehicles using a wideband (broadband/linear) air-fuel ratio sensor on the Bank 1 upstream position. Where P2237 indicates an open (broken) positive current control circuit, P2238 is set when the PCM detects that the voltage or current on that same circuit is abnormally and persistently low — typically the result of a short to ground rather than a complete break. The positive current control circuit is part of the pumping cell control loop that allows the ECU to actively pump oxygen ions in or out of the sensor's internal chamber, measuring lambda continuously across a wide range (typically λ 0.65–1.60) rather than the narrow rich/lean toggle of a conventional narrowband sensor.
When the positive current line is pulled low by a ground fault, the ECU's pumping cell driver reads an implausible current and the lambda signal becomes invalid. The PCM flags P2238, illuminates the MIL, and switches to open-loop fuel control. The most common cause is an internal failure within the sensor itself — the positive current circuit traces on the sensor's internal substrate can short to the sensor body or to the negative circuit. External causes include harness damage where the wire has chafed through to a grounded surface such as the exhaust or a chassis bracket.
Because P2237 and P2238 both relate to the same positive current wire, they can appear together or alternate depending on the nature of the fault (intermittent short vs. open). The diagnostic approach is similar for both: inspect the harness first, test resistance to ground, then verify sensor heater integrity before condemning the sensor itself.
Common causes
Most-frequently reported root causes when P2238 is logged.
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1
Internal short to ground within the wideband sensor's positive current control circuit (most common)
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2
Chafed positive current wire contacting exhaust pipe, heat shield, or chassis ground
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3
Corroded or shorted connector pins at the sensor harness plug
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4
Water or coolant ingress into the sensor connector causing a ground path
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5
Damaged sensor pigtail — pinched or melted insulation creating a ground fault
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6
Failed sensor heater causing thermal damage to internal cell circuitry
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7
PCM output driver fault producing an abnormally low reference (rare)
Symptoms drivers notice
How to diagnose P2238
A typical diagnostic flow when this code is present.
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1
Scan for all DTCs and review freeze-frame; note whether P2237 or heater codes accompany P2238, as co-occurrence narrows the fault location
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2
Inspect the wideband sensor connector and the entire wiring harness for signs of chafing, melted insulation, or contact with the exhaust system where a short to ground is most likely
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3
With the ignition off, measure resistance between the positive current control wire and chassis ground; a low reading (close to 0 Ω) confirms a short to ground
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4
Check each pin in the sensor connector for corrosion, moisture, or backing-out; clean and re-test if contamination is found
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5
Verify sensor heater operation — measure heater element resistance between the heater pins and compare to specification; a failed heater accelerates internal cell degradation
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6
If the wiring and connector are sound, perform an internal sensor resistance check across the positive current terminals; abnormal reading confirms internal sensor failure
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7
Replace the wideband O2 sensor, clear codes, and complete a full drive cycle to verify the repair
Vehicles where we've handled P2238
Platforms in our catalogue with confirmed P2238 coverage.
Related powertrain codes
Frequently asked questions
What is the difference between P2237 and P2238?
Both codes involve the same positive current control circuit of a wideband O2 sensor. P2237 means the circuit is open (broken wire), while P2238 means the circuit voltage is low — typically a short to ground.
Why does P2238 force the engine into open-loop operation?
The wideband sensor's lambda signal is derived from the pump current flowing through the positive current control circuit. If the circuit is shorted low, the PCM cannot reliably measure that current.
Can a bad sensor heater cause P2238?
Indirectly, yes. The wideband sensor's internal cells must reach a precise operating temperature (around 750–780°C) to function correctly.
Is P2238 more expensive to fix than P2195 or P2196?
Generally yes, if the sensor requires replacement. Wideband (broadband) AFR sensors have more complex internal construction than conventional narrowband sensors.
Disabling P2238 in software
RaceTune can permanently disable P2238 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P2238 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C50 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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