1991 Mercury Topaz EGR Pressure Feedback Sensor Replacement Cost

The EGR pressure feedback sensor is used to monitor pressures in the exhaust gas recirculation system, part of the vehicle's emissions control system. With this sensor, the engine control module, or powertrain control module, will monitor EGR pressures, and use that information to regulate that pressure. If any changes are made while monitoring EGR pressures, the sensor will report the new pressure values as confirmation.

EGR pressure feedback sensors use exhaust gas pressure in the EGR system to monitor how much pressure is placed on the EGR system at any given time. This can be helpful for manufacturers and engine control system software designers as a tool to understand how to finely tune the EGR system of the vehicle for changing conditions. At high engine speeds and loads, the EGR system will see higher pressures, and at low engine speeds and loads, the EGR system will see lower exhaust pressures. The engine control software will use the information from the feedback sensor to reduce or increase pressure on the EGR system for the best possible EGR system performance. This is accomplished by opening or closing the EGR valve incrementally until the engine control module is satisfied with the pressure in the EGR system. An easy way to understand the pressure sensor is to consider it a flow sensor for the EGR valve. If the EGR system is flowing at too much or too little exhaust gas, the sensor will allow the ECM notice the fault and prevent damage.

As with any EGR issue, the most common symptoms noticed when the exhaust gas recirculation pressure feedback sensor fails are rough idling, hesitation accelerating from a stop, lack of engine power, misfires, and, of course, illumination of the dreaded check engine light. Hesitation from a stop may also be accompanied by stalling or very low engine speed when slowing the vehicle down, especially from highway speeds. The vehicle may also hesitate for a short or extended time, then accelerate quickly as if the accelerator pedal were pressed to the floor.

Anytime the check engine light comes on, especially if flashing, the vehicle should be seen by a professional, or, at the very least, scanned to identify the on-board diagnostic trouble codes stored in the engine control module. The check engine light should not be ignored, especially if the issue pertains to the EGR system. Not only will a faulty EGR system lead to poor gas mileage and the mentioned symptoms, but it can ultimately lead to failure of the vehicle to start and run.

EGR system failure due to a faulty pressure feedback sensor is very common on many American made vehicles. Otherwise known as the DPFE, the pressure feedback sensor is an electronic component which is subjected to high heat and carbon deposits. They can last for quite some time, but failure is likely.

When incorrect exhaust gas recirculation (EGR) flow rates are noted by the engine control module (ECM), the technician will connect a diagnostic scanner so he or she may understand why the ECM has reported this fault. While reading the readings of the various sensors, the technician may notice that the DPFE (pressure sensor) is reading out of its manufacturer specified range. The technician will then back-probe the signal voltage to ensure the sensor is reporting the voltage read by the ECM, otherwise the ECM could have failed. If the signal voltage is identical to that read by the ECM, and the reference voltage is correct, the sensor will need to be replaced.

Replacing the sensor in most American made vehicles will require two rubber or composite rubber hoses to be removed from the sensor and metal lines from the EGR tube or exhaust manifold. Afterwards, the sensor will be disconnected from its electronic connector, the hoses will be replaced as needed, and the new sensor will be installed. Some models may have the sensor installed with a fastener or clip, and this is a simple matter of removing installation hardware and replacing it for the new sensor.

If the rubber hoses leading to the sensor are cracked, leaking, or otherwise in disrepair, replace them to determine if that is the cause of on EGR leak. In some situations, this may be the case. Also, replace the sensor only after determining it is performing outside of its set parameters, not before. Replacing the sensor without cause may lead to unnecessary financial and time costs.

The EGR system is nearly as hot as the exhaust system, especially if the engine has been running under heavy load or high engine speed. Wait at least thirty minutes to one hour before servicing the system, or just ensure the metal tubes, rubber hoses, and sensor are cool to the touch before proceeding. Some systems will use a sensor that screws into the EGR tube, so ensure you understand which type you have, where it is located, and how it is serviced and tested before attempting diagnosis or replacement.

Diagnosis and replacement of the EGR pressure feedback sensor is not difficult. As long as the EGR system and computerized automotive circuits are understood, this can be done by anyone with a multimeter and a little time to spare. It is important that the DIY mechanic ensure that the specifications for the signal voltage from the sensor for the vehicle being serviced are correct. Some vehicles of the same make and model may have different specifications depending on engine size and year.