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Home / DTC / P2203 — NOx Sensor Circuit High Bank 1 Sensor 1

P2203 — NOx Sensor Circuit High Bank 1 Sensor 1

Detailed page for trouble code P2203.

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Code

P2203

Generic P — Powertrain

NOx Sensor Circuit High Bank 1 Sensor 1

Brand: Generic
Type: P — Powertrain
Views: UK: 16 EN: 18 RU: 15
AI status
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Page language: EN

Causes

  • Failed or internally shorted NOx sensor (Bank 1, Sensor 1)
  • Short to battery voltage on the sensor signal wire
  • Corroded, loose or damaged sensor connector or pins
  • Wiring harness short or damaged insulation (power feeding into signal)
  • Faulty sensor heater circuit backfeeding signal (if combined)
  • Poor ground or high-resistance ground at sensor or ECU

Symptoms

  • Check Engine/MIL illuminated with P2203 stored
  • Possible increased NOx readings or incorrect emissions control behavior
  • Failed emissions/inspection tests (NOx-related)
  • In some systems, reduced engine performance or limp mode if emissions control is affected
  • Possible active regeneration or SCR system warnings on diesel vehicles

What to check

  • Retrieve freeze-frame and readiness data; confirm P2203 is current and note other related codes
  • Visually inspect sensor, connector and wiring at Bank 1 Sensor 1 for damage, corrosion, water intrusion or pin push-out
  • Check for aftermarket repairs or splices in the sensor wiring harness
  • Backprobe the sensor connector with ignition ON (engine OFF) and with engine running; observe signal voltage behavior
  • Check for presence of battery voltage on the signal pin (indicates short to power)
  • Measure continuity and resistance from sensor connector to ECM pin to check for short to power or open circuit

Signal parameters

  • Typical NOx sensor signal: low millivolt/low-voltage output in clean air, increases with NOx concentration (sensor-specific). Expected idle/clean-air values often near 0.1–1.0 V for many designs (manufacturer-specific)
  • High-condition detection: sustained voltage above the sensor's normal operating range or a value near battery voltage indicates a short to +12V or sensor failure
  • Heater supply/monitor: should see battery voltage on heater feed when commanded; heater resistance typically low (a few ohms) — refer to vehicle service data
  • Open-circuit: very high impedance or no response from the sensor; short-to-battery: signal pinned near battery voltage; short-to-ground: signal pinned near 0 V

Diagnostic algorithm

  1. Confirm the code and note any related codes (P2200–P2205, etc.). Record freeze-frame data and live NOx sensor readings if available.
  2. Perform a visual inspection of Bank 1 Sensor 1, its connector, and wiring harness for contamination, corrosion, breaks, or crushed wiring. Repair visible damage before further testing.
  3. With the connector connected, backprobe the signal wire with ignition ON (engine OFF). Observe voltage. If the signal is near battery voltage, suspect a short to power.
  4. Start the engine and observe live sensor signal behavior. A properly working sensor should vary with engine load and exhaust conditions; a constant high voltage implicates wiring or sensor failure.
  5. Remove connector and check for voltage on the signal pin relative to ground. No voltage with connector disconnected plus voltage present with connector connected can indicate backfeed from sensor/heater or internal short.
  6. Inspect and measure heater circuit: verify supply voltage and measure heater resistance to specification. A heater short can affect signal circuitry on some designs.
  7. Check continuity from sensor signal pin to the ECM pin and test for shorts to battery and ground on the harness. Repair any short/open found.
  8. If wiring and connections pass tests, replace the NOx sensor with a manufacturer-approved part and clear codes. Retest and verify the fault does not return.
  9. If the new sensor shows the same symptom and wiring checks good, consider ECM input circuit testing or replacement per manufacturer procedures.

Likely causes

  • Open or shorted signal wire to +12V (most common)
  • Corroded connector causing intermittent high readings
  • Sensor failed due to age, contamination or overheating
  • Heater circuit fault causing unwanted voltage on signal line

Fault status

⚠️ Status
P2203 — NOx Sensor Circuit High (Bank 1 Sensor 1): Sensor signal above expected range; possible short to battery or sensor failure.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P2200 P2201 P2202 P2204 P2205
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