P0470 OBD-II: Exhaust Pressure Sensor "A" Circuit

What does code P0470 mean?

Code P0470 stands for Exhaust Pressure Sensor Malfunction.

Some vehicles (mainly those with turbocharged engines) have an exhaust pressure sensor (EP). This sensor does exactly what the name implies - it measures exhaust backpressure. This information is sent to the vehicle's computer, the powertrain control module (PCM). Knowing the exhaust back pressure helps the PCM determine control of an emissions device called the exhaust gas recirculation valve (EGR). In some cases, the PCM also uses this information as input for turbocharger control.

On most vehicles, the PCM sends the EP a reference voltage. The EP then varies its internal resistance according to exhaust pressure and the modified voltage signal is read by the PCM. A tube connects the EP sensor to the exhaust manifold.

Code P0470 indicates the PCM has detected a problem with the exhaust pressure sensor (otherwise known as the exhaust back pressure sensor).

P0470 symptoms

• An illuminated check engine light
• Engine performance problems
• Unable to perform regeneration (diesel engines)

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Common causes for P0470

Code P0470 is typically caused by one of the following:

• A faulty EP sensor
• A blocked EP sensor tube
• Exhaust system problems
• Wiring issues
• A problem with PCM

How to diagnose and repair P0470

Perform a preliminary inspection

Sometimes P0470 can pop up intermittently. This is especially true if the code is a history code and not current. Clear the code and see if it returns. If it does, the next step is to perform a visual inspection. A trained eye can check for issues such as broken wires and loose connections. The exhaust system and EP tube should also be inspected closely. If a problem is found, the issue should be repaired and the code cleared. If nothing is discovered, check for technical service bulletins (TSBs). TSBs are recommended diagnostic and repair procedures put out by the vehicle manufacturer. Finding a related TSB can greatly reduce diagnostic time.

Check the circuit

The next step is to verify the EP sensor circuit is intact. This can be done using a digital multimeter (DMM). The EP sensor will have three wires going to it: reference, position sense and ground.

The DMM should measure approximately 5-volts coming to the sensor on the reference wire. To check the ground side of the circuit, the DMM should be switched to the ohmmeter setting. Continuity should be measured between the FP sensor ground wire and ground. There should also be continuity between the FP sensor position sense terminal and the PCM.

If an issue is found with any portion of the circuit, the factory wiring diagram will need to be traced pinpoint the problem. Then, the problem can be repaired and the code cleared.

Check the EP sensor

Typically, the next thing a technician will do is check the EP sensor itself. This can be accomplished using a diagnostic scan tool connected to the vehicle diagnostic port. The EP sensor data should be compared to that of the manifold absolute pressure (MAP) and barometric pressure (BARO). If the EP sensor is working properly, its voltage should increase as pressure increases. If not, it's probably faulty and should be replaced.

EP sensor operation can also be checked directly at the sensor using a DMM or oscilloscope fitted with back probe test leads. Once again, the voltage value on viewed on either of these tools should increase as exhaust back pressure increases.

Check the PCM

In rare cases, the PCM may be at fault. The PCM should supply a 5-volt reference to the EP sensor. If it does not, it may be faulty or require reprogramming.

Other diagnostic codes related to P0470

• P0471: Code P0471 indicates the powertrain control module (PCM) has detected an exhaust pressure (EP) sensor range/performance issue
• P0472: Code P0472 indicates the powertrain control module (PCM) has detected a low input signal from the exhaust pressure (EP) sensor. This typically indicates a short circuit.
• P0473: Code P0473 indicates the powertrain control module (PCM) has detected a high input signal from the exhaust pressure (EP) sensor. This typically indicates an open circuit.
• P0474: Code P0474 indicates the powertrain control module (PCM) has detected an intermittent problem with the exhaust pressure (EP) sensor.

Code P0470 technical details

In the case of an out of range high of low EP signal, the PCM will close the EGR system and default the turbocharged to calculated reference values.