P0159

P0159-O2 SENSOR 2/2 SLOW RESPONSE

P0159-O2 Sensor 2/2 Slow Response:

Theory of Operation
The downstream O2 Sensor is located in the exhaust path behind the catalytic converter, is monitored for proper response to assure optimum catalytic converter efficiency. The downstream O2 response monitor is intended to diagnose a downstream O2 sensor that is not moving or stuck in a voltage window and to insure accurate information for catalyst monitor diagnosis.

WHEN MONITORED
Vehicle is started and driven between 20 and 55 MPH with the Throttle open for a minimum of 120 seconds. Coolant greater than 70° C (158° F). Catalytic Converter Temp greater than 600° C (1112° F) and EVAP Purge is active.

SET CONDITION
The oxygen sensor signal voltage switches less than 16 times from lean to rich within 20 seconds during monitoring. Two Trip Fault. Three good trips to turn off the MIL.

POSSIBLE CAUSES
- Exhaust leak
- (K243) O2 2/2 signal circuit
- (K904) O2 return downstream circuit
- O2 sensor

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test

1. ACTIVE DTC

NOTE: Check for contaminants that may have damaged the O2 Sensor: contaminated fuel, unapproved silicone, oil and coolant.

Ignition on, engine not running.

NOTE: After the repairs have been made, verify proper O2 Sensor operation. If all the O2 Sensor voltage readings have not returned to normal, follow the diagnostic procedure for the remaining O2 Sensors.

With a scan tool, read DTCs.

Q: Is the DTC active at this time?

YES: Go To 2
NO: Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Component Tests and General Diagnostics
Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. EXHAUST LEAK

Start the engine.
Inspect the exhaust system for leaks between the engine and the O2 Sensors.

Q: Are there any exhaust leaks?

YES: Repair or replace the leaking exhaust parts as necessary. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 3




3. (K243) O2 2/2 SIGNAL CIRCUIT

Turn the ignition off
Disconnect the 2/2 O2 Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (K243) O2 2/2 Signal circuit in the O2 Sensor harness connector.

Q: Is the voltage between 4.5 and 5.0 volts?

YES: Go To 4
NO: Check the (K243) O2 2/2 Signal circuit for a short to ground, open, or short to voltage. If OK, replace and program the Powertrain Control Module. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test




4. (K904) O2 RETURN DOWNSTREAM CIRCUIT

Measure the voltage on the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.

Q: Is the voltage at 2.5 volts?

YES: Go To 5
NO: Check the (K904) O2 Return Downstream circuit for a short to ground, open, or short to voltage. If OK, replace and program the Powertrain Control Module. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

5. O2 SENSOR

If there are no possible causes remaining, view repair.

Repair
Replace the O2 Sensor. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test