242

Possible Causes

• •Collapsed or restricted air intake duct
• •Dirty or loose ECM grounds
• •Electromagnetic interference (EMI) / ignition noise from open or poor ground circuit in ignition system or ECM
• •Faulty HO2S sensor
• •HO2S sensor not installed securely or wire leads contacting exhaust manifold or ignition wires
• •High fuel pressure due to a faulty fuel regulator or obstructed fuel return line
• •Higher manifold pressure than normal
• •Injector failing in an open manner
• •Plugged air filter
• •Shifted IAT sensor causing ECM to sense lower than actual incoming air temperature
• •Short or unwanted voltage on HO2S connector signal pin B circuit
• •Skewed ECT sensor causing ECM to sense engine temperature colder than actual

Suggested Actions

1. 1Check ECM grounds to ensure they are clean and tight (Refer to Section 1C Engine Electrical Power and Ground Distribution)
2. 2Check ECT sensor
3. 3Check IAT sensor
4. 4Clear DTC information from the ECM using the DST and test run engine to verify repair
5. 5Diagnose and repair any other DTC codes present before proceeding
6. 6Diagnose any other ECM codes that are present before beginning this diagnostic procedure
7. 7Disconnect HO2S sensor and ECM wire harness connectors, key ON, and check for voltage at HO2S connector signal pin B and engine ground using a DVOM; repair circuit as necessary
8. 8Inspect air filter for being plugged
9. 9Inspect air intake duct for being collapsed or restricted
10. 10Perform Fuel System Diagnostics (Refer to Section 1B Fuel System Diagnostics)
11. 11Perform On-Board (OBD) System Check
12. 12Replace HO2S sensor
13. 13Temporarily disconnect the MAP Sensor to allow the ECM to set a default value for MAP
14. 14Verify HO2S sensor is installed securely and wire leads are not contacting exhaust manifold or ignition wires

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