P2431

P2431-SECONDARY AIR INJECTION SYSTEM AIR FLOW SENSOR CIRCUIT PERFORMANCE

Theory of Operation

For 20 seconds following a vehicle cold start, the air injection system delivers a controlled amount of outside air into the exhaust system, upstream of the catalytic converters, in order to help reduce hydrocarbon and carbon monoxide gas emissions.

- When Monitored:
ECT above 0 C (32 F), ambient air temperature within approximately 2 degrees of ECT, actual air flow is less than or equal to model airflow, and Secondary Air Flow diagnostic counter above 100 (approximately 3 seconds). Secondary Air Pump Control circuit active.

- Set Condition:
The PCM detects that the measured air flow is below a calculated minimum value, above a calculated maximum value, or there is no difference between the minimum measured air flow value and the maximum measured air flow value during monitoring.

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure

1. DTC IS ACTIVE

WARNING: The normal operating temperature of the exhaust system is very high. Never work around or attempt to service any part of the exhaust system until it has cooled. Special care should be taken when working near any part of the exhaust system. The temperature rises to a high level after a short period of engine operating time.

NOTE: Diagnose and repair any system voltage or Main Relay circuit DTCs before continuing with this test.

1. Turn the ignition on.
2. With the scan tool, select View DTCs and review the DTC environmental data for this DTC.

Is the good trip counter greater than 0?

Yes

- Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure. Checking for an Intermittent DTC

No

- Go to 2

2. (F342) FUSED MAIN RELAY OUTPUT CIRCUIT OPEN OR HIGH RESISTANCE

1. Turn the ignition off.
2. Disconnect the Air Flow (AF) Sensor connector.
3. Turn the ignition on.
4. Using a 12 volt test light connected to ground, check the (F342) Fused Main Relay Output circuit in the AF Sensor harness connector.

NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.

Is the test light illuminated and bright?

Yes

- Go to 3

No

- Repair the (F342) Fused Main Relay Output circuit for an open circuit or high resistance.
- Perform the PCM Verification Test. PCM Verification Test

3. (K157) AF SIGNAL CIRCUIT VOLTAGE

1. Turn the ignition on.
2. Measure the voltage of the (K157) AF Signal circuit in the AF Sensor harness connector.

Is the voltage between 4.8 and 5.1 volts?

Yes

- Go to 4

No

- Go to 6

4. (K957) AF SENSOR GROUND CIRCUIT TEST

1. Turn the ignition off.
2. Using a 12 volt test light connected to 12 volts, check the (K957) AF Sensor Ground circuit in the AF Sensor harness connector.

NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.

Is the test light illuminated and bright?

Yes

- Go to 5

No

- Go to 9

5. AF SENSOR
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the AF Sensor and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related connectors.
4. Monitor the scan tool data relative to this circuit and wiggle test the wiring and connectors.
5. Look for the data to change or for the DTC to reset during the wiggle test.
6. Search for any Technical Service Bulletins that may apply.

Were any problems found?

Yes

- Repair as necessary.
- Perform the PCM Verification Test. PCM Verification Test

No

- Replace the AF Sensor.
- Perform the PCM Verification Test. PCM Verification Test

6. (K157) AF SIGNAL CIRCUIT SHORTED TO VOLTAGE

1. Turn the ignition off.
2. Disconnect the Powertrain Control Module (PCM) connector.
3. Turn the ignition on.
4. Measure the voltage of the (K157) AF Signal circuit in the AF Sensor harness connector.

Is there any voltage present?

Yes

- Repair the (K157) AF Signal circuit for a short to voltage.
- Perform the PCM Verification Test. PCM Verification Test

No

- Go to 7

7. (K157) AF SIGNAL CIRCUIT SHORTED TO GROUND

1. Turn the ignition off.
2. Measure the resistance between ground and the (K157) AF Signal circuit in the AF Sensor harness connector.

Is the resistance above 100 ohms?

Yes

- Go to 8

No

- Repair the (K157) AF Signal circuit for a short to ground.
- Perform the PCM Verification Test. PCM Verification Test

8. (K157) AF SIGNAL CIRCUIT OPEN OR HIGH RESISTANCE

NOTE: When checking circuits at the Powertrain Control Module (PCM), be careful not to damage or distort the connector terminals. Improper measurement technique could result in poor pin to terminal contact.

1. Measure the resistance of the (K957) AF Sensor Ground circuit between the AF Sensor harness connector and the PCM.

Is the resistance below 5.0 ohms?

Yes

- Go to 10

No

- Repair the (K957) AF Sensor Ground for an open circuit or high resistance.
- Perform the PCM Verification Test. PCM Verification Test

10. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Secondary Air Pump Assembly and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related connectors.
4. Monitor the scan tool data relative to this circuit and wiggle test the wiring and connectors.
5. Look for the data to change or for the DTC to reset during the wiggle test.
6. Search for any Technical Service Bulletins that may apply.

Were any problems found?

Yes

- Repair as necessary.
- Perform the PCM Verification Test. PCM Verification Test

No

- Replace the Powertrain Control Module (PCM).
- Perform the PCM Verification Test. PCM Verification Test