P0172 on Chevrolet: How to Diagnose & Fix

Only the 2000 model year Monte Carlo is named in this NHTSA campaign, and only cars carrying the 3800 V6 (L36) together with one of the affected Delphi fuel pressure regulators. The defect is a leaking regulator, occurring at a much higher rate than normal. Leaked fuel travels through a vacuum line into the intake manifold, where it sits. The danger is confined to a specific sequence: the engine is cranked, it fails to start, and a mistimed spark ignites that fuel. The resulting backfire can rupture the intake manifold. NHTSA describes the follow-on damage as a displaced fuel line that pulls an injector out of place, leaking fuel and creating a fire risk. GM notified owners in two phases starting June 30 and September 30 of 2004. The campaign as a whole covered 910,873 vehicles across all included models.

The 4.3L Vortec V6 used a Central Port Injection system (CPI 1992-1995, CSFI 1996-2002) with a central injector body and six plastic poppet lines — the "spider" — mounted inside the intake manifold. The plastic lines and nut-kit connections crack and leak raw fuel into the plenum, while deposit buildup sticks the poppet valves open or closed, mis-fueling individual cylinders. The result is hard hot starts, persistent misfires, fuel-pressure leak-down, and a rich/fuel-smell condition; GM addressed sticking poppets in TSB 00-06-04-003B by back-servicing the CSFI unit with a redesigned MFI assembly.

The direct-injection fuel injectors on the 1.5L turbo can leak - internally past a cracked injector body/tip (dumping raw fuel into the cylinder and causing a misfire) or externally past worn upper O-rings (fuel smell, weeping at the rail). This is distinct from the covered high-pressure fuel-pump and in-tank fuel-pump-module failures. GM issued a Customer Satisfaction Program for a fuel-injector leak on some 2025 Equinox that directs dealers to replace all four injectors and the fuel feed pipe.

NHTSA lists the 2000 Impala in this recall when it left the factory with the 3800 V6 (L36) and one of the suspect Delphi fuel pressure regulators. Those regulators leak far more often than they should. On the Impala the leaked fuel does not simply drip away — it is drawn into the intake manifold through a vacuum line. Should the engine be cranked and fail to start, the fuel sitting in the manifold can be lit by a mistimed spark and backfire. NHTSA's stated consequence is a ruptured intake manifold, which can in turn displace a fuel line and pull an injector out of its bore, leaking fuel with a possibility of fire. Owner notification went out in phased mailings beginning June 30, 2004, with a second phase on September 30, 2004. Across every model in the campaign, 910,873 vehicles were involved.

GM bulletin 00-06-04-003B covers 1996-2002 Chevrolet C/K models (including Suburban) with CSFI engines such as the 5.7L VIN R (L31): deposit build-up on a CSFI poppet valve ball or seat can make the poppet stick open or closed, mis-fueling that cylinder and causing a misfire, typically as a rough idle after start-up. Similar symptoms have other causes; confirm the engine and installed injection system first.

The 5.7L, 5.0L and 4.3L Vortec engines used a Central Sequential Fuel Injection (CSFI) "spider" assembly with nylon fuel tubes ending in spring-loaded poppet nozzles inside the intake. The poppets clog with carbon or leak/stick open, causing raw fuel intrusion, hard starting/flooding, and misfires. GM acknowledged the problem with special policy 99066 (revision 99066F) for CSFI trucks, and under a California Air Resources Board agreement coverage of the fuel injector system on about 700,000 1996-2001 vehicles was extended to 10 years/200,000 miles.