P045F

Gas Recirculation B Control Stuck Closed

P045F is a generic OBD-II powertrain diagnostic trouble code: Gas Recirculation B Control Stuck Closed. 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
P045F
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
Need P045F disabled?
RaceTune permanently disables any OBD-II trouble code on supported ECUs — for motorsport, off-road, and export use.
→

What P045F means

P045F is an SAE generic powertrain diagnostic trouble code defined as Exhaust Gas Recirculation "B" Control Stuck Closed. The "B" designator identifies the second EGR circuit, which on modern diesel and some petrol engines corresponds to the low-pressure EGR (LP-EGR) valve — the circuit that recirculates cooled exhaust gas from downstream of the diesel particulate filter back into the intake upstream of the turbocharger compressor. The PCM/ECM monitors valve position feedback (typically via a position sensor or calculated flow model) and sets this code when it commands the LP-EGR valve to open but the valve remains in the closed position beyond a calibrated threshold.

A valve stuck closed prevents exhaust gas from being recirculated at low loads, causing combustion temperatures and NOx emissions to rise above legislated limits. On vehicles with active NOx reduction strategies, the ECM may alter fuelling, boost, or SCR dosing to compensate, but tailpipe NOx compliance cannot be maintained. The MIL illuminates on the first or second failed drive cycle depending on the OEM's readiness monitor calibration.

Common root causes include carbon deposit build-up seizing the valve pintle, a failed EGR actuator motor or solenoid, a broken or disconnected position sensor, wiring faults in the "B" circuit, or a cracked/blocked EGR cooler causing excessive back-pressure that physically prevents the valve from opening. Mechanical blockage from heavy soot accumulation is by far the most frequent cause on high-mileage diesel engines.

Common causes

Most-frequently reported root causes when P045F is logged.

  • 1
    Carbon/soot deposit build-up seizing the LP-EGR ("B") valve pintle or bore
  • 2
    Failed EGR valve actuator motor or control solenoid (open-circuit or short)
  • 3
    EGR "B" valve position sensor failure or implausible signal
  • 4
    Wiring harness damage, corroded connector pins, or broken ground in the EGR B circuit
  • 5
    Blocked or collapsed EGR cooler creating excessive back-pressure preventing valve opening
  • 6
    Vacuum supply fault (on vacuum-actuated EGR B valves) — cracked hose or failed solenoid
  • 7
    ECM/PCM software fault or incorrect calibration for EGR B position model
  • 8
    Mechanical seizure due to coolant intrusion from a leaking EGR cooler

Symptoms drivers notice

MIL (check engine light) illuminated
Elevated NOx emissions — likely emissions test failure
Slightly reduced fuel economy at part-load cruise conditions
Possible rough or uneven idle if EGR flow imbalance affects mixture
Increased combustion noise (diesel knock) at light loads due to higher combustion temperatures
No perceptible driveability loss in many cases — code is often a background monitor failure

How to diagnose P045F

A typical diagnostic flow when this code is present.

  1. 1
    Perform a full scan for all stored and pending DTCs; note any companion EGR A, EGR cooler, or boost pressure codes that may indicate a shared root cause
  2. 2
    Command the EGR B valve open/closed using a bi-directional scan tool and monitor the position sensor PID — confirm whether the valve physically moves and whether the sensor tracks the command
  3. 3
    Inspect the EGR B valve, its bore, and the connected pipework for heavy carbon or soot blockage; remove and clean or replace if seized
  4. 4
    Check the EGR B wiring harness and connector for corrosion, pin-back, chafed insulation, or open-circuit resistance; verify 5 V reference and ground at the position sensor
  5. 5
    Test the EGR B actuator coil resistance against the OEM specification; replace the valve assembly if the motor or solenoid is out of spec
  6. 6
    Inspect the EGR cooler for signs of coolant ingestion (white deposit, milky residue) or internal collapse that could back-pressure the valve shut
  7. 7
    Clear the DTC and run the relevant OBD-II EGR readiness monitor drive cycle; confirm the code does not return before completing repairs

Vehicles where we've handled P045F

Platforms in our catalogue with confirmed P045F coverage.

AUDI A4 20D

Related powertrain codes

Frequently asked questions

Can I drive with P045F set?

Yes, in most cases the vehicle remains driveable and does not enter limp mode. However NOx emissions will be elevated, and the vehicle will fail an emissions inspection. Prolonged operation with a stuck-closed EGR valve can also accelerate combustion chamber wear and increase DPF loading on diesel engines, so prompt repair is recommended.

Is P045F the same as P045C or P045D?

No. P045C is 'EGR B Control Circuit Low' and P045D is 'EGR B Control Circuit High' — both are electrical faults in the actuator wiring. P045F specifically means the valve position feedback indicates the valve is mechanically or electrically unable to open (stuck closed), even when the circuit itself may be intact.

What is the difference between EGR A and EGR B?

The SAE 'A'/'B' suffix distinguishes between two separate EGR circuits. 'A' is the primary (usually high-pressure) EGR loop; 'B' is the secondary circuit, most commonly the low-pressure EGR loop found on modern Euro 5/6 and Tier 2/3 diesel engines that recirculates gas from after the DPF back to the turbo inlet.

Will cleaning the EGR valve fix P045F?

On high-mileage diesel engines, carbon-fouled valve seizure is the single most common cause, and thorough cleaning of the valve and its bore often resolves the code. However, if the actuator motor, position sensor, or wiring is also damaged, cleaning alone will not clear the fault. Always verify valve movement with a scan tool after cleaning before reassembling.

Disabling P045F in software

RaceTune can permanently disable P045F — 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 P045F 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 EDC17C74 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.

Got P045F in your scan?

Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.

Upload your file