Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Oxygen Sensor After Catalytic Converter, Checking
Observe all safety precautions: SAFETY PRECAUTIONS
View clean working conditions: CLEAN WORKING CONDITIONS
Prior to repair work, perform a preliminary check to verify the condition. Refer to PRELIMINARY CHECK .
Use only gold-plated terminals when servicing any component with gold-plated electrical harness connector terminals.
For wiring diagrams, component locations, and connector views, Refer to the applicable wiring diagram.
Special tools and workshop equipment required
- Generic scan tool
- Multimeter
- Wiring diagram
Test requirements
- The oxygen sensor properly installed
- Exhaust system free of leaks
- The oxygen sensor fuses OK
- Ground connections between engine/transmission/chassis OK
- Battery voltage at least 12.5 volts
- Coolant temperature at least 80° C
- All electrical consumers switched off
- Vehicles with automatic transmission, shift selector lever in park or neutral
- A/C switched off
- Engine running
The oxygen sensor compares the oxygen content of the outside air with the residual oxygen content in the exhaust gas, and generates a voltage input signal to the engine control module.
If oxygen sensor voltage does not fluctuate, the sensor does not respond, or responds too slowly, the following causes are possible:
Slits in the oxygen sensor tip are plugged
Sensor not up to operating temperature
Sensor has been thermally overloaded
Transition resistance in signal wire or reference ground connection
Sensor has been damaged by electrical contact cleaner or similar contaminant (drawn through signal wire by capillary action due to thermal fluctuation)
Sensor has been damaged by exposure to silicone. When using silicone sprays and sealants, silicone residue is drawn into the engine where it passes unburned into the exhaust and can damage the oxygen sensor
Test procedure
-- Using a generic scan tool, refer to Diagnostic Mode 05 - Read Current System Data.
Mode 05 may not be supported on all systems. On systems where Diagnostic Mode 05 is not supported, refer to Diagnostic Mode 6 for oxygen sensor monitoring test results.
-- Review the mode data test results.
If any of the test results indicate a monitor failure:
-- Refer to the monitor support documentation as indicated in the mode test procedure to diagnose and repair the cause of the failure.
If the test results indicate no monitor failures:
Checking primary voltage
-- Disconnect the oxygen sensor electrical harness connector. Refer to the service information for removal and installation procedures.
-- Switch ignition on.
-- Using a multimeter, measure the voltage between the sensor signal and reference ground circuits.
- Specification: 0.400 to 0.500 V
-- Switch ignition off.
If specified value is not obtained:
-- Check the oxygen sensor wiring and connections.
If specified value is obtained:
-- Replace the oxygen sensor. Refer to the appropriate service information for removal and installation procedures.
Checking wiring and connections
-- Remove the engine control module. Refer to the service information for removal and installation procedures.
-- Using a multimeter, measure the resistance of the signal and reference ground circuits between the oxygen sensor and the engine control module. Refer to the applicable wiring diagram.
Specified value: 1.5 Ω max.
If the specification was not obtained:
-- Check the circuits for a short to each other, short to battery voltage, and short to ground.
-- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
-- Repair the wiring or connection as necessary.
If no malfunction is detected in the wiring:
-- Replace the engine control module. Refer to the service information for removal and installation procedures.
Final procedures
After repair work, the following work steps must be performed in the following sequence:
- Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
- If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
- If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.