P1345, P0440, and P0172 Codes on 2002 GMC Envoy 4.2L: DIY Troubleshooting Without Engine Access
Hello, I'm struggling to diagnose the issue with my 2002 GMC Envoy 4.2L without opening the engine bay. After experiencing rough idling and a sensation that the vehicle might shut down when slowing down or stopping, I pulled up the OBD-II codes using a code reader: P1345, P0440, and P0172. I recently had a professional diagnostic performed—only to find they confirmed exactly what my code reader showed. They suggested two additional tests at $225 each, which I can't afford. I've already replaced both the camshaft and crankshaft position sensors, but that didn't resolve the issue. I also changed the fuel filter. Prior to this problem, the oil was changed and the water pump was replaced due to a failing bearing. Additionally, my SUV has been overheating from a crack near the radiator cap—this occurred during the water pump replacement. Given these circumstances, I suspect the root cause may involve the timing chain or reluctor wheels. One day while driving, the vehicle became extremely hot and oil pressure dropped significantly. When I pulled over and shut off the engine, it made a loud noise and shook violently. I'm wondering if this overheating event caused a timing imbalance, which in turn triggered the P0172 and P0440 codes. I have no formal car knowledge—this issue has only prompted me to research online. I don't have the funds for professional repair services. The vehicle has 220,000 miles and appears to have had five previous owners before me. I've owned it for four months and have changed oil twice. I'm unsure what maintenance was performed by prior owners. Can anyone help clarify what these codes mean in this context? Is a timing chain or sensor issue likely? What are the most cost-effective, DIY steps to diagnose and fix this without engine disassembly?
Start with addressing P1345 before moving to P0172—then tackle P0440, and finally consider the coolant leak. The Variable Cam Timing (VCT) system relies on oil pressure to regulate camshaft timing. Try changing the engine oil and adding one bottle of Risolone oil detergent. This can help dissolve gum buildup in the VCT solenoid. The solenoid is located in the engine head, near where the coolant hose connects—close to the power steering pump. After adding the detergent, start the engine and let it run. As the detergent circulates through the system, it may free up a stuck solenoid. This could help clear the P0172 code. For P0172: NEVER install a K&N air filter—this can cause incorrect airflow readings. Perform a fuel pressure test with the engine off (KOEO). Check for fuel pressure drop under load. Also inspect the vacuum line connected to the fuel pressure regulator—it should not have any fuel in it, as a leak here can cause rich mixtures and trigger P0172.