|Trouble Code||Fault Location||Probable Cause|
|P0470||Exhaust gas pressure sensor -circuit malfunction||Wiring, exhaust gas pressure sensor, ECM|
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What Does Code P0470 Mean?
OBD II fault code P0470 is a generic code that is defined as “Exhaust Pressure Sensor “A” Circuit” , and is set when the PCM (Powertrain Control Module) detects a failure, malfunction, or defect in the reference and/or signal circuit(s) of the exhaust back pressure sensor that is labelled “A”. Note that since some applications may have more than one exhaust backpressure sensors, it is recommended that the manual for the affected application be consulted to locate and identify exhaust backpressure sensor “A” correctly.
Although exhaust backpressure sensors are used on many gasoline-powered applications, this sensor is most commonly found on turbo diesel applications, on which this sensor plays a critical role in emission control. In practice, an exhaust backpressure sensor is used to measure the amount of backpressure in an exhaust system. In most cases, and especially on diesel applications, the amount of exhaust backpressure is directly related to the amount of particulate matter (soot) that is being held captive by the DPF (Diesel Particulate Filter).
Since an excessive amount of soot in the DPF effectively clogs the exhaust system, thus impeding the free flow of exhaust gas through the system, the PCM interprets the actual exhaust back pressure as a measure of how clogged the DPF is. When the PCM deems the DPF to be clogged (based on input data from the exhaust backpressure sensor), it will initiate a process known as DPF regeneration either by injecting a reactant into the exhaust, or by raising the exhaust gas temperature by injecting raw fuel into the exhaust to burn off the accumulated soot.
In terms of operation, the exhaust backpressure sensor is supplied with a 5-volt reference voltage by the PCM. As the pressure in the exhaust changes, the electrical resistance of the sensing element changes as well, with the result that more or less voltage is passed back to the PCM via a dedicated signal circuit, with the changing signal voltage being interpreted by the PCM as changes in pressure.
It should be noted, that on some applications, the input data from the exhaust back pressure sensor is also used by the PCM to monitor/control turbo charger boost pressure, in addition to monitoring / regulating the operation of the EGR (Exhaust Gas Recirculation) system. However, and regardless of the systems the exhaust gas backpressure sensor is associated with on any given application, the PCM depends on reliable, accurate, and plausible input data from the sensor if all associated systems are to work as expected.
Thus, if the PCM detects any malfunction, defect, failure, or fault in the exhaust back pressure sensors’ control / signal system that prevents the exhaust back pressure system from generating, or delivering accurate input data, it recognizes that it cannot monitor the exhaust pressure effectively, and it will set code P0470, and may also illuminate a warning light as a result.
Where is the P0470 sensor located?
The image above shows the location (circled in yellow) of the exhaust backpressure sensor on a 7.3L Ford Powerstroke engine. However, it should be noted that since the location and appearance of these sensors vary greatly between applications and manufacturers, it is strongly recommended that the manual for the affected application be consulted to locate and identify the exhaust backpressure sensor correctly.
Note however, that on many applications it may be necessary to remove or disassemble major, but unrelated parts and components in order to gain access to the sensor. In fact, on some applications it is so difficult to gain access to this sensor that for many non-professional mechanics the better option might be to refer the vehicle to the dealer or other competent repair facility for professional assistance, or diagnosis and repair.
What are the common causes of code P0470 ?
Some common causes of code P0470 could include the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors in the backpressure sensors’ reference and/or signal circuits
- Defective exhaust back pressure sensor
- Clogged or restricted exhaust gas feeding tube (where applicable)
- Boost pressure leaks on applications where this sensor is used for boost pressure control
- Blockages or restrictions in the exhaust system downstream of the back pressure sensor
- Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced