SureTrack Real Fix: Smoke Test to the Rescue

Don’t get distracted by trouble codes indicating a faulty component, proper testing procedures will lead to a successful repair the first time. Follow this Real Fix to see how a technician diagnosed codes P0131, P0171 and P1123 on this Chevrolet Tahoe and found the components that caused the problem.

Vehicle
2005 Chevrolet Tahoe 5.3L

Title
P0131, P0171, P1133, Replaced Intake manifold gasket set, Oxygen Sensor

Complaint
The customer states the check engine light is on.

Cause
Connected a scan tool and found codes: P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1); P0171 – Fuel Trim System Lean (Bank 1) and P1133 – HO2S Insufficient Switching (Bank 1 Sensor 1). With the scan tool connected, performed a road test, monitored live data and found the long term and short term fuel trim was out of specifications and the heated oxygen sensor (B1-S1) signal 0.0 to 1.0 Volt scale parameter was slow to respond when at idle and when the throttle was snapped. Performed a visual inspection of the air intake system and found no apparent faults. Connected a smoke machine to the air intake system, induced smoke into the system and found smoke leaking from the intake manifold gasket indicating a failed intake manifold gasket. Replaced the intake manifold gasket and continued the diagnosis for the heated oxygen sensor (B1-S1). Ran the engine with the vehicle at the normal operating temperature and raised the engine speed to 2,500 RPM. The heated oxygen sensor (B1-S1) signal should cycle between above 800 mV and 250 mV. Monitored the heated oxygen sensor (B1-S1) signal parameter on the scan tool and found the sensor signal parameter switch rate of 3 – 5 times in 5 seconds or 6 – 10 times in 10 seconds did not switch properly.

At idle and 2,500 RPM, used the scan tool to monitor the oxygen sensor (B1-S1) signal specified 0.0 to 1.0 Volts parameter and found the sensor signal parameter remained fixed. From idle, snapped the throttle four times in a row and observed the heated oxygen sensor (B1-S1) voltage did not go negative at full throttle and positive during deceleration. Performed a propane enrichment test at 2,500 RPM, monitored the heated oxygen sensor (B1-S1) signal parameter on the scan tool and found the sensor signal parameter did not respond to the rich fuel mixture condition. Key on, used a multi-meter to check for the presence of 12 Volt supply and less than 100 mV ground at the heated oxygen sensor (B1-S1) connector and found both were present. Disconnected the heated oxygen sensor connector, visually inspected the connector, terminals and wiring harness and found no obvious signs of damage. Used the multi-meter to measure the specified 3 to 15 Ohm resistance of the heated oxygen sensor (B1-S1) heater and found the measured resistance was out specifications. These test results verified the intake manifold gasket and the heated oxygen sensor (B1-S1) were faulty.

Correction
Replaced the intake manifold gasket set and oxygen sensor (B1-S1), cleared codes, performed a road test and verified the vehicle operated properly. The check engine light did not illuminate and no fault codes returned.