P2F85

SCR NOx Catalyst Efficiency Below Threshold - Bank 2

P2F85 is a generic OBD-II powertrain diagnostic trouble code: SCR NOx Catalyst Efficiency Below Threshold - Bank 2. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P2F85
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P2F85 means

P2F85 is the Bank 2 equivalent of P2F84, indicating that the NOx conversion efficiency of the SCR catalyst on the second exhaust bank has fallen below the OBD minimum threshold. This code is relevant only on engines with two separate exhaust banks each fitted with their own SCR catalyst and associated NOx sensors, such as large V6, V8, or V10 diesel engines.

The diagnostic logic mirrors P2F84: the module calculates efficiency from the ratio of pre- and post-catalyst NOx concentrations. A below-threshold result on Bank 2 must be distinguished from a Bank 1 result and may indicate that one catalyst has aged or been damaged while the other remains serviceable. Comparing live NOx data between banks can help isolate whether the issue is catalyst-side or sensor-side.

As with P2F84, related dosing system faults must be excluded before the catalyst is condemned. On dual-bank systems, verify that the Bank 2 DEF injector and dosing module are functioning and that exhaust routing has not introduced cross-bank interference in the NOx sensor readings.

Common causes

Most-frequently reported root causes when P2F85 is logged.

  • 1
    Aged or thermally damaged Bank 2 SCR catalyst.
  • 2
    Sulphur or ash poisoning of the Bank 2 catalyst washcoat.
  • 3
    Bank 2 DEF dosing fault reducing reductant supply to that catalyst.
  • 4
    Failed or drifted Bank 2 upstream or downstream NOx sensor.
  • 5
    DEF contamination affecting the Bank 2 dosing circuit.
  • 6
    Exhaust leak on the Bank 2 side upstream of the SCR catalyst.
  • 7
    Physical catalyst substrate damage from road debris or impact.

Symptoms drivers notice

MIL illuminated alongside a Bank 2 or general SCR warning.
Elevated tailpipe NOx from the Bank 2 exhaust path.
Possible inducement countdown on vehicles with strict NOx regulations.
Asymmetric NOx readings between Bank 1 and Bank 2 on scan tool live data.
No significant driveability change in most circumstances.

How to diagnose P2F85

A typical diagnostic flow when this code is present.

  1. 1
    Scan for all DTCs and compare any Bank 1 vs Bank 2 SCR-related codes.
  2. 2
    Review live NOx sensor data for both banks to determine if the efficiency gap is consistent.
  3. 3
    Verify DEF dosing on Bank 2 by commanded actuation of the Bank 2 injector.
  4. 4
    Check Bank 2 NOx sensors (upstream and downstream) for plausible operation.
  5. 5
    Test DEF concentration for the Bank 2 supply if contamination is suspected.
  6. 6
    Inspect the Bank 2 exhaust for leaks between the dosing point and the catalyst.
  7. 7
    Replace the Bank 2 SCR catalyst only after confirming the dosing system and sensors are functional.

Related powertrain codes

Frequently asked questions

Can P2F84 and P2F85 occur simultaneously?

Yes, on dual-bank diesel engines both catalysts can degrade together or a system-wide issue such as DEF contamination can affect both banks.

Does P2F85 affect the Bank 1 side at all?

No. P2F85 is specific to the Bank 2 exhaust path. Bank 1 catalyst efficiency is monitored separately by P2F84.

Which side is Bank 2 on my engine?

Bank 2 is the cylinder bank that does NOT contain cylinder number 1. Refer to the vehicle-specific service information for the exact physical location on your engine.

Is the repair the same as for P2F84?

The diagnostic and repair process is identical; the only difference is that all checks are directed at the Bank 2 components rather than Bank 1.

Disabling P2F85 in software

RaceTune can permanently disable P2F85 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECUs with a P2F85 disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch MD1CS001 verified 1 software version

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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