P0172 Code on a Cadillac: Fuel Trim System Rich, Bank 1 (Cadillac Guide)

P0172 on a Cadillac is "Fuel Trim System Rich, Bank 1." The engine computer has been pulling fuel out for so long that it has hit its limit, and the mixture is still rich. On the Cadillacs GM has written the most about — the ATS and CTS with the 2.0L turbo — the usual cause isn't a failed part at all: it's gasoline collecting in the engine oil from short trips, and GM says replacing the high-pressure pump or injectors won't fix it unless they're proven faulty. Elsewhere in the lineup GM has documented a leaking high-pressure pump on the Escalade and CTS-V, a leaking intake manifold on the diesel Escalade, and swapped cam actuators on the CT4's 2.7L.

What Does P0172 Mean on a Cadillac?

Your Cadillac's engine control module (ECM) trims fuel using the upstream oxygen or air-fuel ratio sensor. Short-term fuel trim reacts instantly; long-term fuel trim is the correction it learns and keeps. Negative trim means the ECM is removing fuel because the exhaust looks rich.

P0172 sets when bank 1's long-term trim stays at its rich-correction limit. GM's rich test has a twist worth knowing. In GM's 2008 OBD documentation for the 3.6L LY7 — the V6 in mid-2000s CTS, STS and SRX models — the rich test is passive and, if needed, intrusive: when trims look rich, the ECM shuts off EVAP purge and re-checks. Only if the mixture is still rich with purge off does it fail. It is a Type B code, so the check engine light normally needs two failing trips.

That intrusive step tells you something: a P0172 that survives it is not just fuel vapor from the charcoal canister. Something else is adding fuel — and on direct-injected Cadillac engines, one of the most common "something elses" is fuel boiling out of the crankcase oil and being drawn back in through the PCV system.

For a Chevrolet four-cylinder take on the same code, see our P0172 guide for the Chevy Equinox.

Which Cadillacs Set P0172

• Four-cylinder Cadillacs — ATS, CTS and CT6 2.0T (LTG), ATS 2.5L (LCV), XT4, CT4, CT5 and XT5/XT6 2.0T (LSY), CT4 2.7T (L3B): bank 1 is the whole engine. There is no P0175 on a four-cylinder.
• 3.6L V6 Cadillacs — bank 1 is the bank with cylinder 1. On transverse models (2010–2016 SRX, XTS, XT5, XT6) that is the rear bank near the firewall; on longitudinal models (CTS, STS, ATS, CT6, 2004–2009 SRX) it is the passenger side. The bank 2 rich code is P0175.
• Small-block V8 Escalade and CTS-V — bank 1 is the driver's side.
• 3.0L Duramax diesel Escalade (2021 and later) — yes, the diesel sets P0172 too, and GM has a bulletin for it (below).

Fuel in the Oil: ATS and CTS 2.0T

GM bulletin 18-NA-246 (first released August 2018, revised to March 2022) covers the 2013–2019 ATS and 2014–2019 CTS with the 2.0L turbo (LTG), along with Buick, Chevrolet and GMC models sharing the engine. The condition: MIL on with P0172, sometimes with P06DE or P0521. GM's stated cause is driving in short intervals, allowing excessive fuel to collect in the crankcase. The PCV system then feeds that fuel vapor back into the intake and the trims go rich.

The bulletin's correction is unusually direct. GM states that replacing fuel components such as the high-pressure fuel pump or fuel injectors will not correct P0172 under these conditions unless those parts are verified as causing a rich condition.

What the dealer does depends on model year:

• All 2013–2019 model years: an oil and filter change to remove the fuel, then clear the code and road test. GM notes the oil change is necessary to correct the code.
• 2016–2018 model years: ECM reprogramming as well.
• 2016–2019 model years: replacement of the old-style primary PCV valve in the camshaft cover with a revised valve — unless the engine was built on or after May 7, 2019 (engine unit number breakpoint T119127XHXTX0251), which already has the revised valve.

GM also tells dealers that if the customer keeps making frequent short trips, the oil may need changing more often than the oil life monitor suggests. That matters for owners: a Cadillac 2.0T used mostly for short errands may set P0172 again even after a correct repair.

Escalade and CTS-V V8s

A leaking high-pressure fuel pump. GM bulletin 20-NA-200 (September 2020), titled as a diagnostic tip for P0172 and/or P0175, covers the 2015–2019 Escalade 6.2L (L86) and 2016–2019 CTS-V 6.2L (LT4) along with GM's V8 trucks and sports cars. GM's concern is a high-pressure fuel pump leaking fuel into the crankcase. The test: if normal diagnosis doesn't isolate the rich condition, disconnect the dirty-air side of the PCV system, plug the vacuum supply, start the engine and watch closed-loop trims. If they return to normal, the pump is the likely source. GM notes the amount of fuel reaching the crankcase is small, so an oil change may not reveal it — the PCV system draws the mist straight into the intake. (We read this bulletin through a republished copy, not the NHTSA original.)

Airflow across the MAF. PIP5446A covers 2015–2018 Escalade 6.2L and 2016–2018 CTS-V with harsh 1–2 and 2–3 shifts, light-throttle sputter, rough idle and P0101, P0171, P0172, P0174 or P0175. GM's cause is casting flash in the air filter housing near the MAF sensor; the fix is a new lid, checked for flash itself.

Injector flow class. GM bulletin 20-NA-098 covers 2014–2020 GM V8 gasoline engines including Cadillac's L86, LT4 and LTA. After an injector replacement, the wrong flow class can skew fuel trims and set P0172 among other codes. GM's instruction: read the eight-digit number on the injector body, look it up by VIN in the parts catalog, and order the matching service part — or the nominal-flow injector if you can't tell.

CT4 2.7L and the Diesel Escalade

CT4 and CT4-V 2.7L (L3B), 2020–2026. GM preliminary information PIP6115 (May 2026) covers vehicles that set P1101 and/or P0172, stall when taken off idle, won't rev past about 2,500 rpm or won't start after an engine repair that removed the camshaft actuators. GM's cause: the intake and exhaust actuators were installed on the wrong camshafts. The fix is to swap them, confirmed by part number and the "I" or "E" marking on each actuator face. If your CT4's P0172 appeared right after a camshaft carrier reseal or timing work, this is the first thing to check.

Escalade 3.0L Duramax, 2022–2024. Bulletin 22-NA-128 covers the Escalade and GM full-size trucks with the 3.0L diesel (LM2, LZ0) setting P0172 along with P026D, P2459 and/or P2A00. GM's cause is a leak at the intake manifold, found with the component leak test in service information; the fix is a new manifold. Gasoline P0172 advice — fuel in the oil, high-pressure pump checks — doesn't apply to the diesel.

Symptoms of P0172

• Check engine light, often with no other complaint
• Fuel smell from the exhaust or the oil
• Oil level over the full mark and smelling of gasoline (short-trip fuel dilution)
• Poorer fuel economy
• Rough idle, sputter or harsh shifts on the 6.2L (PIP5446A)
• Stall off idle or crank-no-start on a CT4 2.7L after cam actuator work (PIP6115)
• P0175 alongside on a V6 or V8 when the cause is shared

Causes and How to Confirm Each

How Is P0172 Diagnosed?

1. Record all codes and freeze frame. Fix misfire, injector, MAF, MAP and EVAP codes first — GM blocks the fuel trim test while those are set.
2. Note whether P0175 is also set on a V6 or V8. Both banks rich means a shared cause.
3. Pull the dipstick. Overfull oil smelling of fuel on a short-trip 2.0T points straight at 18-NA-246.
4. Ask about recent work. Injector replacement (20-NA-098) or cam actuator removal on a CT4 2.7L (PIP6115) changes the whole diagnosis.
5. Watch live trims at idle and steady cruise, then command EVAP purge off and see whether they recover.
6. Run GM's PCV disconnect test on a 2015–2019 Escalade 6.2L or CTS-V (20-NA-200).
7. Check fuel pressure desired versus actual on direct-injection engines.
8. Inspect the air box on the 6.2L for casting flash near the MAF.
9. Clear codes and drive long enough for the fuel trim monitor to complete — and on a 2.0T, include a longer drive so the oil gets fully hot.

Parts and Cost

GM Documents That Name P0172 on Cadillac Models

Have a dealer check your VIN against current bulletins, recalls and special coverages rather than relying on any article, including this one.

What Other P0172 Pages Get Wrong

• "P0172 means a bad O2 sensor." A sensor reporting rich is usually right. None of the Cadillac documents above fixes P0172 with an oxygen sensor.
• Replacing the pump or injectors on an ATS or CTS 2.0T. GM's 18-NA-246 says that won't fix short-trip fuel dilution unless the parts are proven faulty.
• Assuming an oil change rules out the pump. On the Escalade and CTS-V, GM says a leaking pump may not show up in the oil at all.
• Treating the diesel Escalade like a gas engine. Its documented P0172 cause is an intake manifold leak.
• Overlooking recent repairs. Wrong-class injectors and swapped cam actuators are both GM-documented causes.
• Quoting P0175 for a four-cylinder. ATS, CT4 and XT4 four-cylinders have only bank 1.

Frequently Asked Questions

Is P0172 serious?

Not usually immediate, but a sustained rich mixture dilutes the oil, washes cylinder walls and can overheat the catalytic converter over time. Fix it rather than living with it.

Why does my ATS keep setting P0172?

If it's a 2.0T used mostly for short trips, GM's 18-NA-246 describes exactly that: fuel collects in the oil. A dealer can apply the oil change, software and PCV valve steps for your model year, and more frequent oil changes may be needed if the driving pattern doesn't change.

Will an oil change fix P0172?

For short-trip fuel dilution, it's GM's documented first step. If trims stay rich afterward, keep diagnosing — the PCV test, injectors and pump come next.

My Escalade's oil looks fine. Can it still be the high-pressure pump?

Yes. GM's 20-NA-200 notes that little fuel tends to reach the crankcase, so the oil may look normal. The PCV disconnect test is how GM separates it out.

Can my diesel Escalade set P0172?

Yes. GM's 22-NA-128 covers 2022–2024 Escalades with the 3.0L diesel setting P0172 with other codes, caused by an intake manifold leak.

Can a dirty air filter cause P0172?

A badly restricted intake can push the mixture rich, and it's free to check. On the 6.2L, also look for casting flash in the air box lid per PIP5446A.

Should I try a fuel system cleaner?

It won't fix fuel in the oil, a leaking pump or swapped actuators. Diagnose the cause first.