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P0118 OBD2 Diagnostic Code on 1997 Chevy S10 Pickup 4.3L V6 - How to Fix and Reset MIL

Model: S10 PU Fault Code: P0118 Posted: 2007-09-18 20:49

I own a 1997 Chevrolet S10 Pickup with a 4.3L V6 engine and a persistent P0118 OBD2 fault code. The check engine light (MIL) has not turned off despite replacing the intake manifold temperature sensor, verifying wiring connections, and measuring voltage with the key on—resulting in approximately 4.93 volts. I've also tried two different ECU units with no improvement. The P0118 code indicates an engine coolant temperature sensor (ECT) signal issue or abnormal readings. While I replaced the temperature sending unit, the voltage reading is within expected range (normal values are typically between 4.5 and 5.5 volts), which suggests the sensor may not be the root cause. I'm seeking advice on possible underlying issues such as ground connection problems, engine block integrity, or internal component failure—especially given that this truck has a history of misfires and overheating incidents (including being stranded in a snowstorm). I suspect potential mechanical wear or lifter gallery cracking in the 4.3L V6 engine. Any insights on troubleshooting steps, diagnostics, or recommended repairs would be greatly appreciated.

Related fault codes
P0118
Comments (7)
Anonymous 2007-09-19 08:08

The P0118 code can sometimes stem from a broken ground wire. Please inspect the back of both cylinder heads for corrosion or missing ground straps—these are common in older S10s and can interfere with sensor readings.

Anonymous 2007-09-19 08:24

This appears to be the same truck that previously experienced recurring misfire issues—did you ever respond to our earlier discussion about compression problems? If so, it's likely related to low cylinder pressure, which could contribute to sensor inaccuracies.

Anonymous 2007-09-20 17:26

Jeff Compton: Yes, this is the same truck. The misfire issue was indeed linked to insufficient compression. While I replaced the temperature sensor and measured a stable voltage (~4.93V), the P0118 code persists. I believe the root cause may lie deeper in engine wear or internal damage. I have a spare 4.3L engine that needs rebuilding. My plan is to start with the cylinder heads. If the P0118 code remains after head work, I'll proceed with a full block rebuild—possibly using .030 overbore, Hyperconetic pistons, total seal rings, and new bearings. The ECU has been ruled out as the issue since two different units have produced identical results. I can't believe that one overheating event could cause such widespread problems—but it did happen during a snowstorm when I was stuck in my mother’s driveway. Thanks for your input.

Anonymous 2007-09-20 17:28

If the engine is showing signs of wear or misfire, addressing mechanical issues like cylinder compression and internal component integrity may be necessary before relying on sensor fixes.

Anonymous 2007-09-20 17:45

I agree—consider having the engine block magnafluxed. The 4.3L V6 engines are known for durability but have a weak point in the lifter gallery, especially under thermal stress. These engines were commonly used in power boats and are prone to cracking when exposed to freezing conditions or overheating. This particular 4.3L came from a S10 Blazer—someone I knew personally tested it. It ran smoothly at idle but showed slight smoke during operation, which may indicate early wear.

Anonymous 2007-09-21 06:03

The P0118 code in older 4.3L V6 engines often points to either sensor wiring issues or underlying mechanical problems such as lifter gallery cracks. A magnaflux inspection can reveal hidden internal damage that might not be visible during routine maintenance.

Anonymous 2007-09-21 16:28

Mohawkmtrs wrote: You may want to get the block magnafluxed. The 4.3s are good engines but they are weak in the lifter galley. Those engines are used extensively on power boat and should they freeze, the first place they crack are in the lifter galley. This 4.3 came out of a S10 Blazer. I heard it run ahd was there when he pulled it out. It smocked a little, but not too bad.