Turn ignition switch to OFF position. Ensure suspect HO2S is disconnected. Disconnect PCM connector
(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM,
measure resistance between suspect HO2S SIG circuit, and PWR GND, SIG RTN, VPWR and VREF
circuits at PCM harness connector (both VREF circuits on 150-pin PCM). See PCM HO2S, PWR GND
& VPWR CIRCUIT TERMINAL IDENTIFICATION table. See PCM CONNECTOR
IDENTIFICATION. If all resistance measurements are more than 10 k/ohms, go to next step. If any
resistance measurement is 10 k/ohms or less, repair short between HO2S SIG and PWR GND, SIG RTN,
VPWR or VREF circuit.
84) Check HO2S SIG & SIG RTN Circuits For Open In Harness
Using a DVOM, measure resistance of HO2S SIG, SIG RTN and VPWR circuits between suspect HO2S
harness connector and PCM harness connector. See PCM HO2S, PWR GND & VPWR CIRCUIT
TERMINAL IDENTIFICATION table. See PCM CONNECTOR IDENTIFICATION and Fig. 233.
If all resistance measurements are less than 5 ohms, go to next step. If any resistance measurement is 5
ohms or more, repair open in affected circuit.
85) Check HO2S Circuit Voltage
Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Reconnect
suspect HO2S and PCM harness connectors. Turn ignition switch to ON position. Using scan tool, access
suspect HO2S PID (12 or 22) from PID/DATA MONITOR & RECORD menu. HO2S DTC identification
is as follows:
z
DTCs P0136, P1137 and P1138 are for HO2S-12.
z
DTCs P0156, P1157 and P1158 are for HO2S-22.
Refer to illustrations for HO2S identification. See Fig. 230-Fig. 232 . If HO2S PID voltage is more than
1.5 volts, go to step 88). If HO2S PID voltage is 1.5 volts or less, go to next step.
86) Check HO2S Ground Circuit In PCM
Turn ignition switch to OFF position. Disconnect PCM connector(s). Using a DVOM, measure resistance
between PWR GND and SIG RTN circuits at PCM connector. See PCM HO2S, PWR GND & VPWR
CIRCUIT TERMINAL IDENTIFICATION table. See PCM CONNECTOR IDENTIFICATION. If
resistance measurement is less than 5 ohms, go to next step. If resistance measurement is 5 ohms or more,
replace PCM.
87) HO2S Circuit Check
Ensure ignition switch is turned to OFF position. Reconnect PCM harness connector(s). Disconnect
suspect HO2S connector. Connect a jumper wire between VPWR and HO2S SIG circuits at suspect
HO2S harness connector. See Fig. 233. Turn ignition switch to ON position. Using scan tool, access
suspect HO2S PID (12 or 22) from PID/DATA MONITOR & RECORD menu. If suspect HO2S PID
voltage is more than 1.5 volts, replace faulty HO2S. If suspect HO2S PID voltage is 1.5 volts or less,
NOTE:
HO2S may be displayed as O2S on scan tool.
2003 Ford Pickup F150
2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline