P045C

Gas Recirculation B Control Circuit Low

P045C is a generic OBD-II powertrain diagnostic trouble code: Gas Recirculation B Control Circuit Low. 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
P045C
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P045C means

P045C is a generic SAE OBD-II diagnostic trouble code defined as Exhaust Gas Recirculation (EGR) "B" Control Circuit Low. It is set by the engine control module (ECM) when the feedback voltage on the secondary EGR valve control circuit — designated "B" to distinguish it from the primary "A" circuit — falls below the calibrated minimum threshold. The "B" designation typically refers to the second EGR valve or actuator loop on vehicles equipped with dual EGR circuits, a configuration common on larger displacement diesel engines and some turbocharged petrol engines with high-pressure and low-pressure EGR loops.

The fault is electrical in nature. The ECM commands a position or duty cycle to the EGR "B" valve actuator and monitors the return signal; a low-circuit condition means the measured voltage is too low, which can indicate a short to ground in the control wiring, an open in the feedback/signal wire, excessive resistance, or a failed actuator drawing insufficient current. It belongs to the P045x family alongside P045A (circuit range/performance), P045B (range/performance), and P045D (circuit high).

Because EGR flow directly affects combustion temperature, NOx output, and engine load calculations, the ECM will typically illuminate the MIL and may restrict EGR operation or enter a reduced-performance strategy. Continued operation with an unresolved EGR circuit fault can accelerate intake manifold fouling and may affect turbocharger behaviour on diesel applications.

Common causes

Most-frequently reported root causes when P045C is logged.

  • 1
    Short to ground in the EGR 'B' valve control or signal wiring harness
  • 2
    Open circuit or broken wire in the EGR 'B' actuator feed, control, or feedback line
  • 3
    Corroded, backed-out, or water-damaged ECM or EGR valve connector pins
  • 4
    Failed or seized EGR 'B' valve actuator (solenoid or stepper motor) with abnormal resistance
  • 5
    Faulty EGR position sensor on the 'B' valve returning a voltage below the valid range
  • 6
    Excessive carbon build-up preventing valve movement, causing actuator overcurrent and feedback dropout
  • 7
    ECM internal driver fault (rare) unable to supply correct drive voltage to the 'B' circuit

Symptoms drivers notice

MIL (Check Engine Light) illuminated
Increased exhaust smoke or elevated NOx emissions
Rough idle or hesitation under load due to disabled or stuck EGR flow
Reduced fuel economy caused by less efficient combustion without EGR
Possible activation of reduced-power or limp mode on diesel vehicles with strict EGR monitoring
Failed emissions inspection (MOT/smog test)

How to diagnose P045C

A typical diagnostic flow when this code is present.

  1. 1
    Perform a full scan with a live-data capable scan tool; note all stored and pending codes — pay particular attention to companion P045x or EGR position codes that narrow the fault to sensor vs. actuator
  2. 2
    Inspect the EGR 'B' valve wiring harness and connectors for visible damage, chafing, corrosion, or water intrusion; repair any found issues and recheck
  3. 3
    With the ignition on (engine off), measure the control circuit voltage at the EGR 'B' valve connector using a DVOM; compare against manufacturer specification (typically 5 V reference or PWM supply) to confirm a low-voltage condition
  4. 4
    Disconnect the EGR 'B' valve connector and measure actuator winding resistance; an out-of-range reading (open or dead short) confirms a failed actuator
  5. 5
    Perform a wiring continuity and insulation test between the ECM pin and the EGR 'B' valve connector to locate shorts to ground or high-resistance open circuits
  6. 6
    Visually inspect the EGR 'B' valve for heavy carbon fouling; clean or replace the valve if mechanically seized, then retest the circuit
  7. 7
    If wiring and actuator test good, check ECM connector integrity and consult manufacturer TSBs before suspecting ECM driver failure

Vehicles where we've handled P045C

Platforms in our catalogue with confirmed P045C coverage.

AUDI A4 20D

Related powertrain codes

Frequently asked questions

Can I keep driving with P045C stored?

Short-term driving is generally possible since the engine will run, but it is not recommended. The EGR system is disabled or degraded, increasing NOx emissions and potentially causing rough running or reduced efficiency. On some diesel vehicles the ECM may invoke a power restriction. Have it diagnosed promptly to avoid secondary issues such as intake fouling or turbo stress.

What is the difference between P045C (circuit low) and P045D (circuit high)?

Both codes point to an electrical fault in the EGR 'B' control circuit. 'Circuit Low' (P045C) means the ECM sees a voltage or current signal below its minimum valid threshold — typically a short to ground or a broken feedback wire. 'Circuit High' (P045D) means the signal is above the maximum threshold — typically a short to the supply voltage or a failed open sensor. The same actuator and wiring must be inspected for both, but the direction of the voltage fault guides where to probe first.

Is P045C the same as an EGR valve failure?

Not necessarily. P045C is specifically an electrical circuit fault. The EGR valve itself may be mechanically and electrically intact, with the fault residing in the wiring, connector, or position sensor. Conversely, a seized or heavily carboned valve can cause the actuator to draw abnormal current and trigger the code. Electrical testing should precede component replacement to avoid unnecessarily replacing an expensive EGR assembly.

Which vehicles commonly trigger P045C?

P045C appears most often on vehicles with dual EGR loops: modern Euro 5/6 and EPA Tier 2/3 diesel engines (common on Ford PowerStroke, GM Duramax, Ram/Cummins, VAG TDI, BMW diesel, and Mercedes BlueTEC platforms) that use separate high-pressure and low-pressure EGR circuits. It is less common on petrol engines but can occur on turbocharged GDI engines fitted with LP-EGR for fuel economy. Always check vehicle-specific TSBs, as some manufacturers have issued software or hardware updates for this circuit.

Disabling P045C in software

RaceTune can permanently disable P045C — 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 P045C 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.

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