Fault-code directory · ECU and electrical assessment
A rear oxygen-sensor warning after exhaust work deserves a careful inspection of what was disturbed. The cable may be stretched, a connector may be incompletely seated, or the replacement component may have the wrong electrical characteristics. Timing alone does not prove that the new part caused the fault.
Codes covered
P0136 · P0137 · P0138 · P0139 · P0140 · P0156 · P0157 · P0158 · P0159 · P0160
These groups concern the downstream oxygen-sensor signal on banks 1 and 2. They cover circuit, low-signal, high-signal, slow-response and inactive-signal reports. They should be kept separate from heater-circuit warnings and catalyst-efficiency warnings. Each describes a different observation made by the controller.
Confirm the full description, suffix and reporting module for your vehicle. These are diagnostic starting points, not a parts replacement list.
Evidence that helps narrow the fault
- Record whether the warning first appeared before the exhaust repair, immediately afterwards or only after a longer drive. Keep the old scan if one exists.
- Confirm the fitted part number and the intended sensor position. Compare wiring layout with the vehicle information rather than relying on connector shape alone.
- Check for exhaust leakage near the sensing point and inspect wiring for heat damage. Evaluate the rear signal in its proper relationship to the upstream sensor and catalyst operating conditions.
Choosing the next repair step
Do not replace a catalyst solely because a rear-sensor circuit code is present. Equally, a new sensor will not cure an exhaust leak, a supply problem or a controller input fault. The repair plan should identify whether the concern is the signal circuit, the sensor itself or a separate exhaust-system condition.
Can a universal sensor be connected just by matching wire colours?
Wire colours are not a universal pinout. Compatibility, heater characteristics and the maker’s approved connection method matter. Supply the exact sensor and vehicle details when asking about a recurring warning.
Talk through the fault with AXION
Send the make, model, year, full scan report and a short description of when the fault happens. Include recent repairs or programming attempts. If you do not have a scan, describe the symptoms in your own words.
Workshop assessments are arranged by appointment in Didcot, Oxfordshire. UK-wide postal module testing and remote support are available for suitable work after compatibility and scope are agreed. Please contact us before removing or posting a module.
Assessment options and appointments · Garage and trade support
Related reading
- Several oxygen sensor heater codes appearing together
- Coolant temperature and warm-up faults before changing the thermostat
Reference for generic code terminology: Snap-on diagnostic code reference. Use the manufacturer’s current service information for the actual vehicle and test procedure. This article provides general diagnostic guidance and is not a report of a particular customer repair.