For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P2096: Post Catalyst Fuel Trim System Low Limit Bank 1
DTC P2098: Post Catalyst Fuel Trim System Low Limit Bank 2

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S Signal | P0131, P0137, P2096, P2098 | P0134, P0140 | P0132, P0138, P2097, P2099 | P0133
Low Reference | -- | P0134, P0140 | P0132, P0138, P2097, P2099 | P0133

### Circuit Description

The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio.

Fuel Trim Biasing is used by the ECM to keep the post catalyst HO2S voltage within a range of 580-665 mV as possible. This allows optimal catalyst efficiency under light load conditions, such as at idle or a steady cruise. The ECM constantly monitors how lean or rich the fuel trim bias is commanded, to determine if the fuel trim bias is greater than a calibrated amount.

### Conditions for Running the DTC

• | Before the ECM can report DTC P2096 or P2098 failed, DTCs P0030, P0031, P0032, P0040, P0041, P0050, P0051, P0052, P0131, P0132, P0133, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0155, P0157, P0158, P0160, P0161, P2177, P2178, P2179, 2180, P2187, P2188, P2189, P2190, P2231, P2232, P2234, P2235, P2270, P2271, P2272, and P2273 must run and pass.

• | DTCs P0100, P0101, P0102, P0103, P0420, P0430, P0443, P0458, and P0459 are not set.

• | The engine speed is 1,200-2,920 RPM.

• | The engine load is 17-20 percent and steady.

• | The closed loop fuel control is active for greater than 3 seconds.

• | The front and rear HO2S are in Closed Loop.

• | The calculated exhaust gas temperature is greater than 300°C (572°F).

• | DTCs P2096 and P2098 run continuously when the conditions above have been met for greater than 200 seconds.

### Conditions for Setting the DTC

The post catalyst fuel trim correction factor is biased lean by more than 8 percent of the HO2S signal value for more than 4 seconds or for a cumulative of 50 seconds.

### Action Taken when the DTC Sets

DTCs P2096 and P2098 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P2096 and P2098 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. Ignition ON, observe the scan tool DTC information. Verify DTCs P0137, P0138, or P0140 are not also set.

⇒ | If any of the above DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

Caution: Refer to Road Test Caution in the Preface section.

Important: The rear heated oxygen sensor (HO2S) must be in closed loop for this diagnostic to run. A road load condition is necessary to obtain closed loop.

2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Verify that none of the following conditions exist:

• | Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .

• | Water intrusion in the HO2S harness connector.

• | Low fuel system pressure--Refer to Fuel System Diagnosis .

• | Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Exhaust leaks near the HO2S.

• | Contaminated HO2S - Silicon.

• | Engine vacuum leaks.

⇒ | If you find any of the above conditions, repair as necessary.

2. Ignition OFF, disconnect the harness connector of the appropriate HO2S 2.
3. Ignition ON, verify the appropriate scan tool HO2S 2 voltage parameter is between 350-550 mV.

⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM.

4. Connect the harness connector at the HO2S 2.
5. Engine idling, raise the engine speed above 1,200 RPM for 30 seconds. Verify the appropriate scan tool HO2S 2 voltage parameter is greater than 60 mV.

⇒ | If less than the specified value, replace the HO2S 2.

6. Engine idling, move the appropriate HO2S 1 and HO2S 2 harnesses between the HO2S harness connectors and the ECM. Observe the suspected scan tool HO2S 1 lambda parameter, and the HO2S 2 voltage parameter.

⇒ | If a parameter changes abruptly, repair the harness/connections as necessary.

7. If all circuits/connections test normal, replace the applicable HO2S 1.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

• | Control Module References for engine control module replacement, setup, and programming