For 1990-2009 cars

Refer to

#### HO2S Sensors

Engine Controls Components
Information Sensors
Cruise Control, VSS
MAF Sensor, EVAP System, EGR Valve
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
.

### Circuit Description

To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the Bank 1 HO2S 2 and the Bank 1 HO2S 3 heated oxygen sensors. The Bank 1 HO2S 2 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The Bank 1 HO2S 3 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the Bank 1 HO2S 2 signal will be far more active than that produced by the Bank 1 HO2S 3 sensor. If the Bank 1 HO2S 3 signal voltage remains excessively high for an extended period of time, DTC P0144 will be set.

### Conditions for Setting the DTC

• | No active transmission, TP sensor, EVAP system, EGR, misfire, IAT sensor, MAP sensor, fuel trim, fuel injector circuit, EVAP solenoid ODM, ECT sensor, or MAF sensor DTC(s) present

• | Bank 1 HO2S 3 signal voltage remains above 999 mV during normal closed loop operation.

• | Air/Fuel ratio is between 14.5 to 1 and 14.8 to 1.

OR

Bank 1 HO2S 3 signal voltage remains above 200 mV during deceleration fuel mode operation.

Either condition must be present for at least 5 seconds.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.

• | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using the scan tool.

### Diagnostic Aids

Check for the following conditions:

• | Fuel pressure high - An excessively rich fuel mixture can cause a DTC P0144 to be set. Refer to Chart A-7, Fuel System Diagnosis.

• | Fuel injector(s) faulty - Refer to Chart C-2A, Injector Balance Test.

• | Check the EVAP Canister for Fuel Saturation. If the EVAP Canister is full of fuel, check canister control and hoses. Refer to Evaporative Emission (EVAP) Control System.

• | Disconnect the MAF sensor and see if the rich condition is corrected. If so, replace the MAF sensor.

• | Check for a leaking fuel pressure regulator diaphragm by checking the vacuum line to the fuel pressure regulator for the presence of fuel.

• | An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.

• | Shorted HO2S - If the HO2S is internally shorted the HO2S voltage displayed on the scan tool will be over 1 volt. Try disconnecting the affected HO2S and jumper the HO2S low circuit to ground with the key ON. If the displayed HO2S voltage changes from over 1000 mV to around 450 mV, replace the HO2S. Silicon contamination of the HO2S can also cause a high HO2S voltage to be indicated. This condition is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. If contamination is evident, replace the affected HO2S.

• | Open HO2S Signal or Low Circuit or Faulty HO2S - A poor connection or open in the HO2S signal or low circuit can cause the DTC to set during deceleration fuel mode. An HO2S which is faulty and not allowing a full voltage swing between the rich and lean thresholds can also cause this condition. Operate the vehicle while monitoring the HO2S voltage with a scan tool. If the HO2S voltage is limited within a range between 300 mV to 600 mV, check the HO2S signal and low circuit wiring and associated terminal connections. If the wiring and connections are OK, replace the HO2S.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table:

1. DTC P0144 being set during deceleration fuel mode operation may indicate a condition described in the Diagnostic Aids above. If the DTC P0144 test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.

2. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to the Powertrain On Board Diagnostic (OBD) System Check
2 |

• | Install scan tool

• | Engine at operating temperature

• | Operate vehicle within parameters specified under DTC Will Set When criteria included in Diagnostic Support.

• | Using a scan tool, monitor Bank 1 HO2S 3 voltage.

Does the Bank 1 HO2S 3 voltage remain above the specified value?

999 mV

Go to Step 4

Go to Step 3

3 |

1. Turn ON the ignition switch.
2. Review and record scan tool Fail Records data.
3. Operate vehicle within Fail Records conditions as noted.
4. Using a scan tool, monitor Specific DTC info for DTC P0144 until the DTC P0144 test runs.

Does scan tool indicate DTC P0144 failed?

--

Go to Step 4

Refer to Diagnostic Aids

4 |

1. Disconnect Bank 1 HO2S 3
2. Jumper HO2S low circuit to ground.

Does scan tool indicate Bank 1 HO2S 3 voltage near the specified value?

450 mV

Refer to Diagnostic Aids

Go to Step 5

5 |

1. Turn OFF the ignition switch.
2. Disconnect PCM connector
3. Turn ON the ignition switch.
4. Using a J 39200 Digital Multimeter, measure voltage between the Bank 1 HO2S 3 sensor signal at the PCM harness connector and ground.

Does the Digital Multimeter indicate a voltage above specified value?

999 mV

Go to Step 6

Go to Step 7

6 | Repair short to voltage in the Bank 1 HO2S 3 signal circuit. Refer to Heated Oxygen Sensor (HO2S) Repair in Electrical Diagnosis. Is the action complete? | -- | Go to Step 8 | --
7 | Replace the PCM. Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 8 | --
8 |

1. Turn ON the ignition switch.
2. Review and record scan tool Fail Records data.
3. Clear DTCs
4. Operate vehicle within Fail Records conditions as noted.
5. Using a scan tool, monitor Specific DTC info for DTC P0144 until the DTC P0144 test runs.

Does scan tool indicate DTC P0144 failed this ignition?

--

Go to Step 2

System OK