P1138 — 13 documented meanings by make
Documented by: ALFA ROMEO, AUDI, BMW, CHEVROLET (USA), CHRYSLER, CITROEN, FIAT, FORD, JAGUAR, LANCIA, MAZDA, OPEL / VAUXHALL, PEUGEOT, PORSCHE, SAAB, SEAT, SKODA, SUZUKI, VOLKSWAGEN — the meaning can differ between manufacturers
P1138 does not mean the same thing on every car — manufacturers reuse the number for different faults. 19 makes document it: Alfa Romeo, Audi, BMW, Chevrolet (USA), Chrysler, Citroen, Fiat, Ford, Jaguar, Lancia, Mazda, Opel / Vauxhall, Peugeot, Porsche, Saab, SEAT, Skoda, Suzuki, Volkswagen. Find your make below.
| Make | Documented meaning | Points at |
|---|---|---|
| Alfa Romeo | HO2S Insufficient Switching Sensor 1 | |
| Peugeot | HO2S Insufficient Switching Sensor 1 | |
| Audi | Bank 2, mixture adaptation, system too lean | |
| SEAT | Bank 2, mixture adaptation, system too lean | |
| Skoda | Bank 2, mixture adaptation, system too lean | |
| Volkswagen | Bank 2, mixture adaptation, system too lean | |
| BMW | Oxygen sensor heater circuit, low voltage, bank 1 sensor 2 | oxygen sensor · signal too low |
| Chevrolet (USA) | Heated oxygen sensor, high voltage during deceleration fuel cut-off | oxygen sensor · signal too high |
| Chrysler | Oxygen sensor heater 2/1 element resistance out of range | oxygen sensor · range or performance |
| Citroen | High pressure rail sensor fault | signal too high |
| Citroen | Lack of heated oxygen sensor 2 switching, sensor indicates rich | oxygen sensor |
| Fiat | Fuel pressure | fuel supply |
| Lancia | Fuel pressure | fuel supply |
| Ford | Lack of heated oxygen sensor, 1/2 switches - sensor indicates rich | oxygen sensor |
| Jaguar | Lack of heated oxygen sensor, 1/2 switches - sensor indicates rich | oxygen sensor |
| Mazda | Lack of heated oxygen sensor, 1/2 switches - sensor indicates rich | oxygen sensor |
| Opel / Vauxhall | Oxygen sensor deceleration fuel cut-off rich, bank 1, sensor 2 | oxygen sensor |
| Porsche | Oxygen sensor range 1, cylinder 4-6 | oxygen sensor |
| Saab | Additive adaptation, bank 2, minimum value air/fuel mixture too rich | |
| Suzuki | Fuel pressure regulator circuit | fuel supply |
P1138 on BMW
On BMW vehicles P1138 is documented as: Oxygen sensor heater circuit, low voltage, bank 1 sensor 2. P1138 is stored when the ECU sees signal too low on oxygen sensor (bank 1, sensor 2). That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.
Usually one of: High resistance in the supply or ground path, dragging the signal down; Corroded connector adding resistance the module reads as a low reading; Sensor drifted out of tolerance with age; Partial short to ground somewhere in the signal line.
Check first, cheapest first:
- Read the live value on a scanner and compare with a known-good reading
- Clean and re-seat the connector, then re-test before replacing anything
- Check the ground point for that circuit — a poor ground causes this far more often than a bad sensor
- Measure the sensor against specification with the connector back-probed
- Replace the sensor only once the wiring and ground have been ruled out
Related BMW codes:
P1138 on Chevrolet (USA)
On Chevrolet (USA) vehicles P1138 is documented as: Heated oxygen sensor, high voltage during deceleration fuel cut-off. P1138 is stored when the ECU sees signal too high on oxygen sensor. That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.
Usually one of: Open ground for the sensor, letting the signal float up; Signal line shorted to a supply voltage; Sensor failed open, which the module reads as maximum; Connector fault interrupting the return path.
Check first, cheapest first:
- Read the live value and compare with what the conditions should produce
- Check the sensor ground continuity back to the module
- Unplug the sensor: if the reading changes, the wiring is intact and the sensor is suspect
- Inspect the connector for corrosion or a spread terminal
- Replace the sensor once ground and signal wiring are confirmed good
Related Chevrolet (USA) codes:
P1138 on Chrysler
On Chrysler vehicles P1138 is documented as: Oxygen sensor heater 2/1 element resistance out of range. P1138 is stored when the ECU sees range or performance on oxygen sensor. That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.
Usually one of: Sensor reading is inside its electrical range but does not match reality; Contamination or deposits changing what the sensor sees; A mechanical fault upstream that the sensor is correctly reporting; Sensor drifted with age without failing outright.
Check first, cheapest first:
- Compare the live value against a second sensor or a known-good figure — this code is about plausibility, not a dead circuit
- Look for the mechanical cause first: leaks, restrictions or wear that would genuinely produce this reading
- Clean the sensor if it is the type that fouls
- Check freeze-frame data to see under what conditions it triggered
- Replace the sensor only after the mechanical side is ruled out
Related Chrysler codes:
P1138 on Citroen
On Citroen vehicles P1138 is documented as: High pressure rail sensor fault; Lack of heated oxygen sensor 2 switching, sensor indicates rich. P1138 is stored when the ECU sees signal too high on the circuit named in the code. That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.
Usually one of: Open ground for the sensor, letting the signal float up; Signal line shorted to a supply voltage; Sensor failed open, which the module reads as maximum; Connector fault interrupting the return path.
Check first, cheapest first:
- Read the live value and compare with what the conditions should produce
- Check the sensor ground continuity back to the module
- Unplug the sensor: if the reading changes, the wiring is intact and the sensor is suspect
- Inspect the connector for corrosion or a spread terminal
- Replace the sensor once ground and signal wiring are confirmed good
Related Citroen codes:
P1138 on Fiat, Lancia
On Fiat, Lancia vehicles P1138 is documented as: Fuel pressure. P1138 points at fuel supply. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.
Usually one of: Fuel filter blocked; Pump worn and no longer making pressure; Pressure regulator faulty; Wiring or relay fault to the pump; Blocked strainer in the tank.
Check first, cheapest first:
- Measure actual fuel pressure against specification — this code is about pressure, so guessing without a gauge wastes parts
- Replace the fuel filter if it is due; it is the cheapest thing in the circuit
- Check the pump relay and its supply voltage
- Listen for the pump priming when the ignition is switched on
- Replace the pump once the filter, wiring and regulator are ruled out
Related Fiat, Lancia codes:
P1138 on Ford, Jaguar, Mazda
On Ford, Jaguar, Mazda vehicles P1138 is documented as: Lack of heated oxygen sensor, 1/2 switches - sensor indicates rich. P1138 points at oxygen sensor. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.
Usually one of: Sensor aged and slow to respond; Heater element failed inside the sensor; Wiring or connector fault at the sensor; Exhaust leak near the sensor drawing in air; Engine genuinely running rich or lean.
Check first, cheapest first:
- Read the sensor's live trace — a lazy or flat signal identifies an aged sensor without removing anything
- Check for exhaust leaks upstream of the sensor
- Inspect the connector, which sits in a hot and exposed place and corrodes
- Measure the heater resistance against specification
- Replace the sensor once the exhaust and wiring are ruled out
Related Ford, Jaguar, Mazda codes:
P1138 on Opel / Vauxhall
On Opel / Vauxhall vehicles P1138 is documented as: Oxygen sensor deceleration fuel cut-off rich, bank 1, sensor 2. P1138 points at oxygen sensor (bank 1, sensor 2). The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.
Usually one of: Sensor aged and slow to respond; Heater element failed inside the sensor; Wiring or connector fault at the sensor; Exhaust leak near the sensor drawing in air; Engine genuinely running rich or lean.
Check first, cheapest first:
- Read the sensor's live trace — a lazy or flat signal identifies an aged sensor without removing anything
- Check for exhaust leaks upstream of the sensor
- Inspect the connector, which sits in a hot and exposed place and corrodes
- Measure the heater resistance against specification
- Replace the sensor once the exhaust and wiring are ruled out
Related Opel / Vauxhall codes:
P1138 on Porsche
On Porsche vehicles P1138 is documented as: Oxygen sensor range 1, cylinder 4-6. P1138 points at oxygen sensor (cylinder 4). The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.
Usually one of: Sensor aged and slow to respond; Heater element failed inside the sensor; Wiring or connector fault at the sensor; Exhaust leak near the sensor drawing in air; Engine genuinely running rich or lean.
Check first, cheapest first:
- Read the sensor's live trace — a lazy or flat signal identifies an aged sensor without removing anything
- Check for exhaust leaks upstream of the sensor
- Inspect the connector, which sits in a hot and exposed place and corrodes
- Measure the heater resistance against specification
- Replace the sensor once the exhaust and wiring are ruled out
Related Porsche codes:
P1138 on Suzuki
On Suzuki vehicles P1138 is documented as: Fuel pressure regulator circuit. P1138 points at fuel supply. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.
Usually one of: Fuel filter blocked; Pump worn and no longer making pressure; Pressure regulator faulty; Wiring or relay fault to the pump; Blocked strainer in the tank.
Check first, cheapest first:
- Measure actual fuel pressure against specification — this code is about pressure, so guessing without a gauge wastes parts
- Replace the fuel filter if it is due; it is the cheapest thing in the circuit
- Check the pump relay and its supply voltage
- Listen for the pump priming when the ignition is switched on
- Replace the pump once the filter, wiring and regulator are ruled out
Related Suzuki codes:
Which one is yours
A generic OBD reader gives you the number, not which of these meanings your manufacturer assigned to it. To get to the specific one:
- Use a brand-specific scanner — VCDS for VAG, INPA or ISTA for BMW, XENTRY for Mercedes, Forscan for Ford. It shows the manufacturer's own text rather than the generic one.
- Read all stored codes together — the neighbouring ones usually point at which system is involved and narrow the list.
- Check freeze-frame data: the RPM, temperature and load at the moment it triggered indicate which system was active.
- If you have no brand scanner, tell me the make and model below and I will tell you which of these applies to your car.
Code family
P1xxx is manufacturer-specific code (VW/Audi, BMW, Mercedes, Toyota etc. have different meanings for the same code number).
Severity
Manufacturer-specific codes need a brand scanner (VCDS for VAG, INPA for BMW, STAR for Mercedes).
That is what holds for P1138 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.
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Code breakdown
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