P2099 Code on a GMC: Post Catalyst Fuel Trim High Limit, Bank 2 (GMC Guide)

P2099 on a GMC is GM's "Post Catalyst Fuel Trim System" code for bank 2 — the oxygen sensor behind the bank 2 catalytic converter keeps reporting a mixture the engine computer cannot correct, and the slow post-catalyst trim has hit its limit. It only exists on GMCs with two exhaust banks: the Sierra, Yukon and Savana V8s, the 4.3L V6, and the V6 Acadia, Terrain and Canyon. Which direction it means depends on the year: GM's 2012–2018 GMC tables call it "High Limit Bank 2 (Too Lean)," and its 2019 and 2020 tables call it "Too Rich Bank 2." The GMC surprise is in bulletin 20-NA-098: on 2014–2020 Sierra, Yukon, Savana and Sierra HD V6s and V8s, GM found P2099 and misfire codes caused by the wrong flow-class injector installed during an earlier repair.

What Does P2099 Mean on a GMC?

Each bank of a V6 or V8 GMC has its own front and rear oxygen sensors. The front sensor runs the fast main fuel trim for that bank. The rear sensor — Bank 2 Sensor 2, after the bank 2 converter — feeds a slow correction GM calls the post-catalyst integral offset, which nudges the front control so the converter stays at its best balance. Zero means balanced. A rear sensor reading lean drives the offset positive (more fuel); one reading rich drives it negative.

When that offset uses "all or most" of its authority in one direction and stays there, a code sets. In GM's 2017 table for group 03 — the Sierra and Yukon 5.3L (L83) and 6.2L (L86), the Sierra 4.3L (LV3), the Savana 4.8L, and the Acadia, Terrain and Canyon 3.6L — P2099 sets when the average integral offset reaches +90% or more and the average total offset is at or above 0%, averaged over 45 seconds. It uses the same enable conditions as P2098, and like the bank 1 codes it is a Type B code that runs in cruise and acceleration, not at idle.

P2099 is the bank 2 twin of P2097. If both set together, look for something both banks share. If only P2099 sets, the cause is usually on bank 2 itself: one injector, one exhaust joint, one sensor.

Lean, Rich, and the 2019 Flip

Here is what the GMC engine tables we checked actually call P2099:

• 2011 (truck group 07: Sierra, Savana, Yukon XL V8s): no P2099 — no post-catalyst fuel trim codes in that file at all.
• 2012 (truck group 07): "Post Catalyst Fuel Trim System High Limit Bank 2 (Too Lean)," same as the bank 1 lean fault.
• 2014 (group 08: Gen V Sierra and Yukon 4.3L, 5.3L, 6.2L) and 2017–2018 (groups 03 and 03A): "High Limit Bank 2 (Too Lean)," indicating "a lean exhaust gas condition."
• 2019 (group 03B: Sierra, Yukon, Acadia and Canyon V6s and V8s; group 03C: Savana and Sierra HD 6.0L) and 2020 (group 03D: Savana 4.3L/6.0L, Sierra HD 6.6L): "Post Catalyst Fuel Trim System Too Rich Bank 2," indicating "a rich exhaust gas condition" at the low limit.

We have not found a GM document that explains the change, so we report it as the tables show it. The practical rule:

• 2012–2018 GMC: P2099 means the bank 2 rear sensor sees lean — air getting in, or not enough fuel.
• 2019 and later: do not assume. Read the bank 2 fuel trims and the Bank 2 Sensor 2 voltage in freeze-frame and live data, and follow the service information for your VIN.

The data always wins: a rear sensor sitting low with positive bank 2 trims is lean; one sitting high with negative trims is rich.

Which GMCs Set P2099

Only GMCs with a V6 or V8 can set P2099. From GM's tables and bulletins:

• Sierra 1500 4.3L V6 and 4.8L, 5.3L and 6.2L V8s (2012 on)
• Yukon and Yukon XL 5.3L and 6.2L
• Sierra HD gas 6.0L and 6.6L (L8T)
• Savana 4.3L, 4.8L and 6.0L
• Acadia 3.6L, Terrain 3.0L and 3.6L (2010–2017), and Canyon 3.6L (2015 on) — plus the Canyon 5.3L V8 (LH9) listed in GM's 2012 truck group

It does not apply to the four-cylinder Terrain, Acadia 2.5L, Canyon 2.5L or Sierra 2.7L turbo, the 2004–2012 Canyon 2.9L four and 3.7L five-cylinder (one bank each), the Duramax diesels, or the Hummer EV.

Where Bank 2 Is on a GMC

• Sierra, Yukon, Savana V8 and the 4.3L V6: bank 1 is the driver's side, so bank 2 is the passenger side. The P2099 sensor is in the passenger-side pipe after that side's converter.
• Acadia and Terrain 3.6L (transverse): bank 1 is the rear bank toward the firewall, so bank 2 is the front bank, toward the radiator.
• Canyon 3.6L (longitudinal): GM numbers cylinder 1's bank as the right bank viewed from the flywheel end, which would make bank 2 the driver's side. Trace the harness from the sensor before you buy.

The Injector-Matching Bulletin

GM bulletin 20-NA-098 (May 2020) applies to V6 and V8 gasoline engines only, and its list includes 2014–2020 GMC trucks with the 4.3L (LV1, LV3), 5.3L (L82, L83, L84), 6.2L (L86, L87, L8B) and 6.6L (L8T). It names P0300–P0308, P050D, P0171, P0172, P0174, P0175, P2099, P219A and P219B.

GM's finding: after an engine repair that required a new injector, it has "seen cases of the incorrect fuel injector being installed in the suspect cylinder," which can skew long- and short-term fuel trims and bring on the check engine light or a rough idle. The reason is how the rails are built. At the supplier, each rail can carry nominal, low or high flow injectors, chosen to balance flow across the rail for emissions. Replacement injectors and kits carry different part numbers from the injectors in the rail.

GM's procedure:

1. Read the 8-digit part number printed on the body of the injector being replaced.
2. Enter the VIN in the parts catalog, go to the fuel injector rail section, find that body number in the description column, and order the service part number listed beside it. GM's example is a 2016 Silverado 5.3L L83, where body number 12668390 maps to service part 12698484.
3. If the original injectors were removed or mixed up and you cannot tell which went where, order the "NOM FLOW" injector part number in the quantity needed.

What that means for a GMC owner: if P2099 or a bank 2 trim code showed up after a misfire repair or injector replacement on a 2014–2020 Sierra, Yukon or Savana, ask whether the replacement injector was matched by its body number. It is a parts-catalog question, not a new diagnosis.

The Acadia, Terrain and Canyon V6 Playbook

GM preliminary information PIP4964F (April 2025), "SES Light With A P2097 Or P2099," covers the 2008–2023 Acadia 3.6L, the 2010–2017 Terrain 3.0L and 3.6L, and the 2015–2022 Canyon 3.6L. GM's order of work:

1. Injectors. GM says the most common concerns "has been related to fuel injectors" and to perform an injector balance or AFIT test before going further. The balance test is not available on the 2009 Acadia.
2. A small exhaust leak, "usually at the outlet to the engine converter," which pulls air in and causes "a false lean concern at the post O2 sensor." Apply air at 5 to 8 psi to the rear of the downstream converter or the tailpipe, then soap the gasket areas and the O2 boss. Leaks that cause the code make larger bubbles; foam is normal. GM warns not to use full shop air, because converter and engine damage can result.
3. The valvetrain — a sticking valve, or a lifter follower off the camshaft — which may or may not cause a misfire.

Nowhere in that sequence does GM replace the rear oxygen sensor or the catalytic converter.

Symptoms of P2099

• Check engine light on — often with no drivability change (PIP4964F)
• Rough idle or misfire codes if a wrong or failing injector is involved (20-NA-098)
• Bank 2 lean code P0174 or rich code P0175 alongside, depending on direction
• Exhaust ticking or puffing on the bank 2 side if a joint is leaking
• P2097 at the same time if the cause affects both banks

Causes and How to Confirm Each

How Is P2099 Diagnosed on a GMC?

1. Check the VIN and the repair history. A recent injector or misfire repair on a 2014–2020 V6 or V8 truck points at 20-NA-098.
2. Fix bank 2 oxygen sensor, heater, misfire and EVAP codes first.
3. Note the model year — lean on 2012–2018 labels, rich on 2019-and-later labels — then confirm with data.
4. Compare bank 1 and bank 2 trims. A one-bank problem points at that bank's injectors, joints or valves.
5. Run an injector balance or AFIT test.
6. Confirm injector part numbers by body number against the VIN parts catalog if any were replaced.
7. Pressure-test the exhaust at 5–8 psi and soap the bank 2 converter outlet and O2 boss.
8. Consider the valvetrain on a V6 if nothing else is found, then clear and cruise to re-run the monitor.

Parts and Cost

GM Documents That Name P2099 on GMCs

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

What Other P2099 Pages Get Wrong

• "P2099 always means rich." On 2012–2018 GMCs, GM's tables say "Too Lean." The label flips to "Too Rich" from 2019.
• Applying it to four-cylinder GMCs. A Terrain 2.4L or Canyon 2.5L has no bank 2.
• Treating every injector as interchangeable. GM's 20-NA-098 says rails mix nominal, low and high flow injectors — order by body number.
• Blasting the exhaust with shop air. GM specifies 5–8 psi and warns against full shop air.
• "Replace the catalytic converter." None of GM's P2099 documents does.

Frequently Asked Questions

Is P2099 serious on a GMC?

Usually not urgent — GM's V6 bulletin describes it with no drivability concerns. But a lean injector, a leak or a valvetrain fault on bank 2 is worth fixing before it becomes a misfire or cooks the converter.

Which side is bank 2 on my Sierra or Yukon?

The passenger side. Bank 1, with cylinder 1, is the driver's side on GMC V8s and the 4.3L V6.

Does P2099 mean rich or lean?

On 2012–2018 GMCs, GM's tables say lean ("High Limit Bank 2, Too Lean"). On 2019-and-later tables it reads "Too Rich Bank 2." Bank 2 fuel trims and rear O2 voltage settle it.

P2099 showed up after my injector was replaced. Coincidence?

Maybe not. GM's 20-NA-098 covers exactly this on 2014–2020 GMC V6 and V8 trucks: a replacement injector of the wrong flow class can skew fuel trims and set P2099. The fix is the injector that matches the original's body number.

My Acadia has P2099. Where do I start?

PIP4964F says injectors first (balance or AFIT test), then a small exhaust leak at the converter outlet using 5–8 psi air and soapy water, then the valvetrain.

What's the difference between P2099 and P2097?

Same test, different bank. P2097 is bank 1 and P2099 is bank 2; both point the same direction for a given model year.

Is there a related bank 2 guide?

Yes. Our GMC P0430 guide covers the bank 2 catalyst test that depends on the same rear sensor.