P2C7A Diesel NOx catalyst (SCR) efficiency below threshold on bank 1, catalyst 2

SCR NOx catalyst efficiency below threshold, bank 1 catalyst 2

Severity not verified — if the car runs badly, have it inspected

No manual or reference giving a driving limit was found; GM bulletins describe a lit warning and an ECM calibration, while owner complaints mention limp mode.

It gets more serious if:

  • Inspect soon: Inspect soon if the truck goes into reduced power or limp mode, or the downshifting or towing behaviour changes.

Source: how we rate severity

P2C7A in short

P2C7A means the diesel exhaust SCR NOx catalyst is not cleaning up emissions as well as the computer expects. On 2020-2023 GM half-ton diesels, GM bulletins point to an ECM calibration. Owners also report repeated NOx converter or EGR valve replacement. Ask a dealer about open software before replacing parts.

The SCR system injects diesel exhaust fluid and uses a catalyst to cut NOx. The computer compares NOx readings from before and after the catalyst, and P2C7A sets when the catalyst is not reducing enough.

GM has issued preliminary information and bulletins for 2020, 2022 and 2023 Silverado and Sierra 1500 diesels that say the cause was under investigation and then that an ECM calibration corrects P2C7A.

Owners on 2020 Sierra 1500 report repeated NOx converter and EGR valve replacements without a lasting fix, so check software before parts.

Most likely causes

  1. Engine computer calibration needing an update

    Supported by vehicle data
    Why it ranks here
    GM PIP5682 says a calibration is being developed for P2C7A on 2020 trucks, PIP5888A says there is an ECM calibration to correct it on 2022 trucks, and 23-NA-193 covers 2023 trucks.
    What would change this
    Rises if the VIN is covered and the calibration is not current. Falls if it is current.
    How to test the engine control module (ecm / pcm)

  2. SCR NOx catalyst or sensor failing

    Supported by vehicle data
    Why it ranks here
    Owners on 2020 Sierra 1500 report the NOx converter replaced more than once, and the readout on a 3.0L Duramax names the code as an SCR catalyst efficiency fault.
    What would change this
    Rises if NOx readings before and after the catalyst are almost equal. Falls if the catalyst cleans normally.

  3. EGR valve fault affecting NOx levels

    Possible — needs testing
    Why it ranks here
    Two Sierra owners report the EGR valve replaced along with the NOx converter. EGR affects engine-out NOx, but no bulletin names it for this code.
    What would change this
    Rises if the EGR valve sticks or its flow is off. Falls if flow is normal.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all codes and note whether P14D9, P20EE, P11D5 or P2383 are stored with P2C7A.

    Low riskTool: OBD-II scan tool

    • IfP14D9 stored too on a 2020 or 2022 truck

      It meansBulletins PIP5682 and PIP5888 pair them.

      Go to step 2

    • IfOnly P2C7A

      It meansAsk about bulletins.

      Go to step 2

  2. Ask a dealer whether your VIN has an open ECM calibration for P2C7A before any parts are replaced.

    Low risk

  3. Have the NOx sensor readings before and after the SCR catalyst compared, and the DEF dosing and EGR flow checked.

    Best left to a shopTool: scan tool with live data

    Warning:Diesel exhaust parts are hot and DEF is corrosive. Leave this to a shop.

Symptoms

  • Check engine light or an emissions warning
  • Reduced power or limp mode Gets more serious: stop and have it checked.
  • Unusual downshifting when towing

Compare with: Check engine light with loss of power

How to fix

  1. Ask a dealer whether your VIN has an open ECM calibration or warranty coverage for P2C7A.

On your vehicle

Chevrolet

  • 2020–2023 · Silverado 1500

    Supported by vehicle data

    GM bulletins PIP5682, PIP5888A and 23-NA-193 cover P2C7A on 2020, 2022 and 2023 diesel trucks; an ECM calibration is the stated fix on 2022.

  • PIP5682 (chevrolet)Status unverified

    P2C7A and/or P14D9 may set

    2020silverado-1500 · NHTSA 10167421

    Preliminary information: clearing procedure and ECM calibration under development.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PIP5888A (chevrolet)Status unverified

    ECM calibration to correct P2C7A

    2022silverado-1500 · NHTSA 10227657

    ECM calibration available.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 23-NA-193 (chevrolet)Status unverified

    DTCs P20EE, P22FE, P2C7A and others

    2023silverado-1500 · NHTSA 10245255

    Repair information for a concern with several diesel DTCs.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

  • 2020 · Sierra 1500

    Supported by vehicle data

    Owners report the NOx converter and EGR valve replaced more than once. Complaint signal only.

  • PIP5682 (gmc)Status unverified

    P2C7A and/or P14D9 may set

    2020sierra-1500 · NHTSA 10167421

    Preliminary information: clearing procedure and ECM calibration under development.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PIP5888A (gmc)Status unverified

    ECM calibration to correct P2C7A

    2022sierra-1500 · NHTSA 10227657

    ECM calibration available.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 23-NA-193 (gmc)Status unverified

    DTCs P20EE, P22FE, P2C7A and others

    2023sierra-1500 · NHTSA 10245255

    Repair information for a concern with several diesel DTCs.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

No curated relationships for P2C7A yet.

All Diesel emissions and glow plugs codes

P2C7A questions

Will replacing the NOx converter fix P2C7A?

Not always. GM bulletins point to an ECM calibration on 2020-2023 trucks, and owners report repeated converter replacements. Ask about software first.

Sources and review

  1. GM PIP5888A: ECM calibration to correct P2C7A (2022 Silverado/Sierra 1500) — General Motors / NHTSA
  2. NHTSA complaint ODI 2098431: 2020 GMC Sierra 1500, NOx converter and EGR valve — NHTSA Office of Defects Investigation (owner complaint)
  3. GM PIP5682: P2C7A and/or P14D9 may set; ECM calibration under development (2020 Silverado/Sierra 1500) — General Motors / NHTSA
  4. GM 23-NA-193: DTCs P20EE, P22FE, P2C7A and others (2023 Silverado/Sierra 1500) — General Motors / NHTSA
  5. NHTSA complaint ODI 2147424: 2020 GMC Sierra 1500, NOx converter and EGR valve — NHTSA Office of Defects Investigation (owner complaint)
  6. NHTSA complaint ODI 2157829: 3.0L Duramax, P2C7A — NHTSA Office of Defects Investigation (owner complaint)
  7. NHTSA complaint ODI 2202167: 2021 Chevrolet Tahoe, P11D5, P14D9, P2383, P2C7A — NHTSA Office of Defects Investigation (owner complaint)
Last reviewed
Written by
Saurabh K.
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