P1131 Possible Causes
- Faulty upstream oxygen sensor, bank 1
- High or low fuel pressure
- Dirty/faulty MAF sensor
- Engine vacuum leak
- Leaking fuel injector or fuel pressure regulator
- Faulty powertrain control module (PCM)
How to Fix Code P1131?
Start by checking the “possible causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
Technical Notes
The code means the powertrain control module (PCM) has detected a lean system, meaning there is not enough fuel or an excessive amount of air in the system. Start by checking for vacuum leaks.
Possible Symptoms
- Check engine light on (or service engine soon warning light)
P1131 Meaning
The Heated Oxygen Sensor (HO2S) monitor is an integrated strategy designed to monitor the HO2S sensors for malfunction or deterioration that could affect emissions. Under specific conditions, the upstream fuel control or HO2S sensors are checked for proper output voltage and response rate (the time it takes to switch from lean to rich or rich to lean). The downstream HO2S sensors used for Catalyst Monitor are also monitored for proper output voltage. An input is required from engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), mass air flow (MAF), throttle position (TP), and crankshaft position (CKP) to activate the HO2S monitor. The fuel system monitor and misfire detection monitor must also have completed successfully before the HO2S monitor is activated.
• The HO2S sensor detects the oxygen content in the exhaust stream and delivers a voltage between zero and 1.0 volt. At stoichiometric lean (air/fuel ratio of about 14.7:1 for gasoline engines), the HO2S will generate a voltage between zero and 0.45 volt. At stoichiometric rich, the HO2S will generate a voltage between 0.45 and 1.0 volt.
• The HO2S monitor evaluates both the upstream (fuel control) and downstream (catalyst monitor) HO2S for proper operation.
• Once the HO2S monitor is activated, the amplitude of the upstream HO2S signal voltage and the response frequency are checked. Excessive voltage is determined by comparing the HO2S signal voltage to a maximum threshold voltage that can be calibrated.
• A fixed frequency closed-loop fuel control routine is executed and the upstream HO2S voltage amplitude and output response frequency are observed. A sample of the upstream HO2S signal is evaluated to determine if the sensor is capable of switching or has a slow response rate.
• An HO2S heater circuit fault is determined by turning the heater on and off and looking for a corresponding change in the OSM and
measuring the current through the heater circuit.
• The MIL is activated after a fault is detected on two consecutive OBD II drive cycles.