P047C

Exhaust Pressure Sensor B Circuit Low

P047C is a generic OBD-II powertrain diagnostic trouble code: Exhaust Pressure Sensor B 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
P047C
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P047C means

P047C is a generic powertrain code that belongs to the auxiliary emission control group. It is stored when the ECU sees a signal from the second exhaust pressure sensor, designated sensor B, that is lower than the sensor circuit is allowed to produce under any real operating condition. It is an electrical circuit fault rather than a judgement about the exhaust system itself: the ECU is reporting that the voltage arriving on the signal wire has fallen below the bottom of the valid measuring window.

Exhaust pressure sensors are almost exclusively found on diesel engines, where the ECU uses exhaust back pressure to manage turbocharger boost control, EGR flow, and diesel particulate filter loading and regeneration. Where two sensors are fitted, sensor A is normally the one nearer the turbine or upstream of the aftertreatment, and sensor B is the second sensor further along the exhaust circuit. The ECU also carries out a plausibility check at key-on, when exhaust pressure should sit close to intake manifold and ambient pressure. If sensor B reads implausibly low at that point, or drops out of range while running, the monitor fails and the code sets.

Because the low reading is characteristic of a short to ground on the signal line, an open reference feed, or a sensor that has failed internally, P047C is usually chased as a wiring and connector problem first. Soot-blocked or cracked pressure pipes and corroded connectors near the hot exhaust are common on high-mileage diesels.

Common causes

Most-frequently reported root causes when P047C is logged.

  • 1
    Short to ground or chafed insulation in the exhaust pressure sensor B signal wire.
  • 2
    Corroded, wet, or loose connector at the sensor, which sits in a hot and dirty area of the engine bay.
  • 3
    Failed exhaust pressure sensor B with an internally shorted or open element.
  • 4
    Open or high-resistance sensor reference voltage feed or ground from the ECU.
  • 5
    Blocked, cracked, or disconnected pressure pipe or fitting feeding the sensor, giving an implausibly low reading.
  • 6
    Wiring harness damage from exhaust heat, vibration, or a previous exhaust or turbo repair.
  • 7
    Water ingress into the harness connector causing a low-side leakage path.
  • 8
    Rarely, a failed ECU driver or reference circuit for that sensor channel.

Symptoms drivers notice

Check engine light on, often with a stored or pending exhaust pressure code.
Noticeably reduced power or a flat, unresponsive throttle if the engine goes into a reduced-power mode.
Black smoke, rough running, or a loss of boost because the ECU cannot trust its exhaust pressure input.
Diesel particulate filter warning appearing later, as regeneration is inhibited while the fault is present.
Higher than usual fuel consumption.
Failed emissions or annual roadworthiness test because of the illuminated warning lamp.

How to diagnose P047C

A typical diagnostic flow when this code is present.

  1. 1
    Read all stored and pending codes and record the freeze frame, so you know whether the fault appeared cold, hot, or under load.
  2. 2
    View live data for both exhaust pressure sensors with the engine off and the key on, and compare them with barometric and manifold pressure, which should all read close together at rest.
  3. 3
    Inspect the sensor, its pressure pipe, and its connector for soot blockage, cracks, corrosion, water, or heat damage.
  4. 4
    Back-probe the connector to confirm the sensor is receiving its reference voltage and has a clean ground path before condemning anything.
  5. 5
    Wiggle-test the harness while watching live data to catch an intermittent short or open, paying attention to sections routed near the exhaust or turbo.
  6. 6
    Disconnect the sensor and check whether the reading moves to the opposite fault extreme, which separates a shorted signal wire from a failed sensor.
  7. 7
    Repair whatever the tests identified, clear the code, and drive the vehicle through a full warm-up and load cycle to confirm the monitor passes.

Related powertrain codes

Frequently asked questions

Can I keep driving with P047C?

Short trips are usually possible, but the ECU has lost a signal it uses to manage boost, EGR, and particulate filter regeneration. Many diesels respond by cutting power, and a filter that cannot regenerate will eventually block. Get it looked at rather than ignoring it.

Will this code fail an emissions test?

Yes, in most regions. P047C is an emission-related powertrain code and turns the check engine light on, which is an automatic fail on any test that includes an OBD readiness check.

Is it expensive to fix?

Often it is not. A surprising share of these faults turn out to be a corroded connector, a soot-blocked pressure pipe, or a chafed wire, which are cheap repairs. A replacement sensor is a moderate parts cost, and only harness or ECU work becomes genuinely expensive.

Why does my scan tool only mention sensor A when the code says B?

Naming varies between manufacturers. Sensor A is normally the upstream exhaust pressure sensor and B the second one further downstream, but you should confirm against the vehicle's own wiring diagram before testing, since some makes label them differently.

Disabling P047C in software

RaceTune can permanently disable P047C — 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.

ECU families we can disable P047C on

We hold the DaVinci A2L disable definitions for these families, so the exact P047C path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.

  • Bosch MD1CP002 verified
  • Bosch MD1CS001 verified

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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