DTC P0031: O2 Sensor Heater Circuit Low 1/1 Or DTC P0032: O2 Sensor Heater Circuit High 1/1: Testing
NOTE:
1/1 HO2S may also be referred to as an upstream oxygen sensor. On 2.5L and 4.0L Federal models, 1/1 HO2S is located in exhaust downpipe in front of catalytic converter. On 4.0L Calif. models, 1/1 HO2S is located in front exhaust manifold.
- Turn ignition on. Using scan tool, actuate HO2S HEATER TEST and monitor 1/1 HO2S voltage for 5 minutes. If voltage changes to about zero volts, go to next step. If voltage does not change to about zero volts, go to step 3 .
- At this time, conditions for DTC to set do not exist or fault is an intermittent problem. Check for any contaminates that may have damaged the 1/1 HO2S such as contaminated fuel, unapproved silicone, oil and coolant. Repair any problems that are found. If no problems are found, start engine and allow it to idle. Ensure engine is at normal operating temperature. Using scan tool, monitor 1/1 HO2S voltage while wiggling connectors and wiring harness from 1/1 HO2S to Powertrain Control Module (PCM). PCM is located on firewall in right rear corner of engine compartment. If voltage changes while wiggling connectors and wiring harness, repair connectors and wiring harness where wiggling caused voltage to change. If voltage does not change, review FREEZE FRAME data using scan tool. Attempt to duplicate condition that caused DTC to set by paying special attention to the conditions during which 1/1 HO2S is monitored. Check for any related technical service bulletins that may apply. Visually inspect related connectors and wiring harness. Repair connectors and wiring harness as necessary. See WIRING DIAGRAMS article. If no problems are indicated, test is complete.
- Disconnect 1/1 HO2S connector. Measure resistance between Orange/Dark Green and Brown/Orange wires at 1/1 HO2S connector (component side). If resistance is not 4-5 ohms with HO2S at 70°F (21°C), replace 1/1 HO2S. If resistance is 4-5 ohms, 1/1 HO2S heater element is okay. Go to next step.
- Measure voltage between ground and Orange/Dark Green wire at 1/1 HO2S harness connector. If voltage is more than 12 volts, go to next step. If voltage is 12 volts or less, repair open power circuit to 1/1 HO2S heater. See WIRING DIAGRAMS.
- Disconnect Powertrain Control Module (PCM) connectors. PCM is located on firewall in right rear corner of engine compartment. Inspect connectors for damaged pins, corrosion and loose terminals. Repair connectors as necessary. If connectors are okay, measure resistance of Brown/Orange wire between 1/1 HO2S harness connector and terminal C8 at PCM C3 harness connector. See Fig 1 . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Brown/Orange wire.
- Measure voltage between ground and terminal C8 (Brown/Orange wire) at PCM C3 harness connector. If no voltage is present, go to next step. If any voltage is present, repair short to voltage in Brown/Orange wire between 1/1 HO2S and PCM.
- At this time, PCM is assumed to be defective. Replace PCM.