← Back to list

P0135 O2 Sensor Heater Fault in 2003 Chevy S10 4.3L Vortec - No Start, Rough Idle, Low Oil Pressure

Model: 03 Chevy s10 4.3 Vortex Fault Code: P0135 Posted: 2016-01-23 12:19

I own a 2003 Chevrolet S10 4.3L Vortec 2WD truck and recently it has stopped starting altogether. Prior to this, the vehicle exhibited rough idling and sputtering. I've already performed a full tune-up including spark plugs, ignition wires, distributor cap, rotor, fuel filter, air filter, and PVC valve. Despite these repairs, the issue persists. The truck now only starts when the gas pedal is held down firmly—otherwise it fails to start. When idling, the oil pressure drops to 20 psi (normally around 40 psi), indicating a potential underlying problem. Using a GM Tech 2 scanner, I've retrieved diagnostic code P0135: 'O2 Sensor Heater Circuit Malfunction - Bank 1, Sensor 1'. During scanning, the MAF sensor reading was recorded at 4.9 g/s, which appears reasonable for a 4.3L engine under idle conditions. I'm considering replacing the IAC valve, but I'm hesitant to continue spending money on parts without clear evidence of failure. I am not an experienced mechanic and would appreciate expert advice on what steps to take next—especially given that the truck is now completely unstartable without flooring the gas pedal.

Related fault codes
P0135
Comments (4)
Anonymous 2016-01-23 12:30

Can you check the IAC valve position readings? If not, try cleaning the IAC valve and throttle body first before replacing it. A MAF reading of 4.9 g/s at idle is within expected range for a 4.3L engine.

Anonymous 2016-01-23 12:49

The IAC position value reported was 226, which seems high for an idle condition.

Anonymous 2016-01-23 14:46

A complete no-start issue with only P0135 present—no other related codes—is concerning. Based on your description, there's no strong evidence pointing to MAF or IAC failure. Start with fundamental checks: fuel delivery and spark. You have a scanner—check the fuel trims (FTs). High FT values may indicate fuel system issues. As a precaution, also inspect engine oil for signs of gasoline contamination.

Anonymous 2016-01-23 17:19

The statement 'the truck only starts when holding down the gas pedal' suggests it might be clearing excess fuel from the system. When flooring the throttle, the IAC valve may be opening fully and allowing sufficient airflow to initiate combustion. Note that a normal idle IAC position should typically be 50 or less when warm—226 is unusually high. As suggested by Kev2, reviewing fuel trims could provide more insight into whether there's an underlying fuel delivery issue.