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P047C Exhaust Pressure Sensor B Low Input

OBD-II Trouble Code Technical Description

Article by
Randy
Randy Worner
ASE Certified Master Technician

Exhaust Pressure Sensor "B" Low Input

What does that mean?

This generic powertrain/engine diagnostic trouble code applies to all engines that use variable nozzle turbochargers (gas or diesel), starting around 2005 on Ford trucks equipped with 6.0L diesel engines, all Ford EcoBoost engines, and eventually leading to the Cummins 6.7L in 2007, the 3.0L in the Mercedes lineup in 2007 and here recently the Cummins 3.0L 6 cyl in the Nissan pickups starting in 2015. That's not to say you wouldn't necessarily get this code in a VW or other make though.

This code is strictly concerned about the incoming signal from the exhaust pressure sensor not matching intake manifold pressure or ambient air pressure at key on. This is strictly an electrical circuit fault.

Code P047B may also be present at the same time as the P047C. The main difference between these two codes is P047C is only electrical while P0471 can be the result of a mechanical or electrical fault. It is typically recommended to start with the P047C (electrical) first before moving on to the P047B (electrical/mechanical) next. This way, if the problem is electrical, there is a higher probability of repair by starting with the electrical.

Troubleshooting steps may vary depending upon manufacturer, gas or diesel, type of exhaust pressure sensor and wire colors. Refer to a vehicle specific repair guide to determine which is the "B" sensor for your particular vehicle.

A typical exhaust pressure sensor:
Exhaust Pressure Sensor

Related exhaust pressure sensor "B" trouble codes:

Symptoms

Symptoms of a P047C engine code may include:

Potential Causes

Typically the causes for this code to set are:

Diagnostic and Repair Procedures

A good starting point is always a technical service bulletin (TSB) search for your particular vehicle. The vehicle manufacturer may have a PCM flash/reprogram to cover this issue, and it pays to check on this before you find you’ve gone down a long/wrong path.

Next, the locate Exhaust Pressure Sensor on your particular vehicle. Once located, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burn spots or melted plastic. Pull the connectors apart and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt or possibly green in color versus the normal metal color you are probably used to seeing. You can get some Electrical Contact cleaner at any parts store if cleaning of the terminals is needed. If this is not possible, find some 91% rubbing alcohol and a light plastic bristle brush to clean them with. Afterwards let them air dry, get some dielectric silicone compound (same stuff they use for light bulb sockets and spark plug wires) and put some where the terminals come into contact.

If you have a scan tool, clear the diagnostic trouble codes from memory, and see if this code returns. If it does not, then the connections were most likely your problem.

If the code does return, we will need to test the sensor and its associated circuits. Typically there are 3 wires at the Exhaust Pressure sensor.

Disconnect the harness going to the Exhaust Pressure Sensor. With a Digital Volt Ohm Meter (DVOM), test the 5V power supply circuit going to the sensor to insure it is being powered up (Red lead to the 5V power supply circuit, black lead to a good ground). If there is 12 volts to the sensor when there should be 5 volts, repair the wiring from the PCM to the sensor for a short to 12 volts, or possibly a bad PCM.

If that’s OK, with a DVOM, check to make sure you have 5V on the Exhaust Pressure Sensor signal circuit (Red lead to the sensor signal circuit, black lead to a good ground). If there is no 5 volts to the sensor, or if you see 12 volts to the sensor, repair the wiring from the PCM to the sensor, or once again a possible bad PCM.

If that’s OK, with a DVOM, check to make sure you have 5V on the Exhaust Pressure Sensor signal circuit (Red lead to the sensor signal circuit, black lead to a good ground). If there is no 5 volts to the sensor, or if you see 12 volts to the sensor, repair the wiring from the PCM to the sensor, or once again a possible bad PCM.

If all tests have passed so far, and you continue to get a P047C code, this would most likely indicate a failed Exhaust Pressure sensor, although a failed PCM could not be ruled out until the sensor had been replaced.

Related P047C DTC Discussions

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