P0172 on GMC: How to Diagnose & Fix
System Too Rich (Bank 1)
2 GMC models · 2 documented issues · 1 critical · $80-$250 repair
P0172 on GMC by model: symptoms, diagnosis and fix
The fuel pressure regulator diaphragm ruptures. Because the regulator is housed inside the intake on the 4.3L CSFI engine, raw fuel is dumped directly into the intake. Causes rich running, hard hot starts, and fuel smell. Can flood the engine with fuel.
Common Symptoms
- Hard starting when hot
- Strong fuel smell
- Black smoke from exhaust
- Fuel pooled in the intake around the regulator
How to Fix
Replace the fuel pressure regulator. On the 1996-2001 4.3L CSFI engine it is housed inside the intake with the main injector, so the upper intake plenum must be removed (aftermarket regulators and reconditioned injector assemblies cost less than the dealer assembly). Before removing the plenum, take off the manifold tuning valve on top of the intake and inspect the regulator area. Fuel lying in the intake, or an unusually clean area around the regulator, points to a leaking diaphragm. Replace the upper plenum gasket when reassembling.
Sources for this issue (2)
On 1.5L LYX-equipped Terrains the charge air cooler outlet tube can separate from the throttle body inlet. The retaining clip design does not hold the duct under boost pressure and heat cycling, so the tube pops off, dumping boost and unmetered air. GM issued Service Update N192266090 (dealer-inventory vehicles only, expired September 30, 2020) and emission recall N192271200 for customer vehicles covering the charge air cooler duct disconnect at the throttle body on 2019 Malibu, Equinox and Terrain 1.5L vehicles, and the condition is further covered by field bulletins PIP5651 and 22-NA-224 across the 2018-2022 range. The cooler itself is fine; the connection has come apart.
Common Symptoms
- Sudden loss of power while driving
- Reduced engine power message
- Check engine light
- Loud whoosh or rushing air sound from engine bay
- Rough idle or stall at low speed
How to Fix
Inspect the outlet duct and throttle-body connection, reseat the duct and install the improved retainer when the duct and sealing surfaces remain serviceable. Replace a damaged duct rather than relying on the clip alone, and have the dealer check the VIN for open emission recall N192271200 (the earlier service update N192266090 applied only to unsold dealer inventory).
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine GM 84828210 charge-air-cooler retainer (supersedes 13434668)$4
2018-2022 GMC Terrain 1.5L turbo branch covered by the service procedure. The OEM catalog also lists the 1.6L diesel, but this issue record is the LYX 1.5L; inspect the duct before ordering.
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Sources for this issue (5)
- GM Service Update N192266090 - Charge Air Cooler Duct Disconnect at Throttle Body (NHTSA TSB PDF)tsb
- GM Emission Recall N192271200 - 2019 Terrain charge air cooler outlet ducttsb
- Disconnected Charge Air Cooler Outlet Air Tube - GM TechLinkarticle
- GM Service Bulletin 22-NA-224 (NHTSA PDF)tsb
- Here's Why Your GMC Terrain May Have Reduced Engine Power - GM Authorityarticle
P0172 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0172 mean on a GMC?
P0172 stands for "System Too Rich (Bank 1)." P0172 means the engine computer has determined the air/fuel mixture on bank 1 is too rich — there is too much fuel relative to air. The PCM watches the oxygen sensors and fuel trims; when it must repeatedly cut back fuel to compensate for an over-rich condition and hits its correction limit, it sets this code. Bank 1 is the side of the engine containing cylinder number one. You may notice poor fuel economy, rough idle, a sulfur/rotten-egg smell, black exhaust smoke, or fouled spark plugs. On GMC it is documented across 2 models: Jimmy, Terrain.
What are the most common causes of P0172?
The most common causes of P0172 are: Dirty or faulty mass airflow (MAF) sensor, Leaking or stuck fuel injector, High fuel pressure (faulty regulator), Faulty oxygen sensor giving skewed readings, Clogged or dirty air filter, Leaking evaporative purge valve adding fuel vapor, Engine coolant temperature sensor reading too cold, Worn spark plugs causing inefficient combustion. The specific cause varies by vehicle.
How much does it cost to fix P0172 on a GMC?
Published repair estimates on GMC range from $80 to $250 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.