Diesel Particulate Filter Pressure Sensor 'A' Circuit Low
The PCM has detected an abnormal voltage reading (high or low) from the diesel particulate filter pressure sensor circuit. Diesel particulate filter pressure is monitored exclusively in vehicles equipped with diesel engines. "Sensor A" indicates a particular sensor. Consult the manufacturer's service manual (or equivalent) for the location of this particular sensor.
Code Set Parameters
Diesel particulate filter pressure is monitored by the diesel particulate filter pressure sensor. The 5-volt (maximum) variable resistance circuit supplies input voltage to the PCM. The PCM calculates the desired diesel particulate filter pressure using input data from the throttle position sensor, mass air flow sensor, tachometer, etc. Actual diesel particulate filter pressure is then compared with desired diesel particulate filter pressure. Variations that exceed the manufacturer's recommended diesel particulate filter pressure will result in a stored trouble code and an illuminated service engine soon lamp. If the diesel particulate filter sensor circuit voltage falls below .022 psi at idle (consult the manufacturer's service manual for the specs on your particular application) a code will be stored and a service engine soon lamp will be illuminated. If the diesel particulate filter pressure sensor signal value at part load is less than a minimum value (or greater than a maximum value) when the engine is running a code will be stored and a service engine soon lamp will be illuminated. Minimum and maximum reference values are based on overall exhaust volume.
If this code is stored in the PCM, the malfunction indicator lamp should be illuminated. Chances are that there will be no other symptoms associated with this type of code other than the possibility of other related trouble codes.
In most cases, this code is caused by a clogged diesel particulate filter or defective diesel particulate filter pressure sensor. However, technicians also report that damaged and burnt electrical wiring and connectors are a possibility. Other causes may include a cracked, loose, or disconnected hose to the diesel particulate filter pressure sensor. The PCM could also be faulty but this is highly unlikely.
The diesel particulate pressure sensor is frequently replaced in error when a clogged or restricted filter is the culprit.
- The diesel exhaust after treatment system consists of an underhood pre-catalyst and an underbody catalyst
- The underbody catalytic converter also consists of the main diesel oxidation catalyst and the coated diesel particulate filter
- The main function of the diesel particulate filter is to collect particulates from the engine exhaust in order to minimize the discharge of pollutants in the atmosphere
- Pollutants (seen as soot particles) accumulate in the channels of the DPF and are burned off at regular intervals through a process called regeneration
- This prevents the diesel particulate filter from immediately clogging
- The PCM commands diesel particulate filter regeneration after calculating various vehicle conditions such as diesel particulate filter pressure variations, exhaust gas temperature, engine oil quality, engine speed, etc
- Excessive accumulation of pollutants in the diesel particulate filter can cause a drop in engine performance
- During regeneration, additional fuel is injected via multiple post injections in order to increase the exhaust gas temperature
- The diesel particulate filter temperature is increased to approximately 1,110°F during this process and the accumulated pollutants are oxidized or burned off into carbon dioxide.
The diesel particulate filter pressure system uses a variable capacitance sensor to monitor diesel particulate filter pressure and input data to the PCM
- The PCM calculates the desired amount of diesel particulate filter pressure by considering inputs from various other engine and drivability sensors
- The actual diesel particulate filter pressure sensor voltage (varies between manufacturer's) is then compared with the manufacturer's recommended diesel particulate filter pressure sensor voltage
- If these two readings fail to coincide a code will be stored.
If there are other turbocharger or exhaust codes, diagnose and repair them before attempting to diagnose this code
- Several tools may be needed to successfully diagnose this code if no exhaust leaks are detected
- A suitable scanner (or code reader), a digital volt/ohmmeter, and a manufacturer's service manual (or the equivalent) will be most helpful in performing a successful diagnosis
- An infrared thermometer with a laser pointer can also be an asset.
Begin with a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- Continue by clearing the code and operating the vehicle to see if it returns
- This will help to determine whether or not the malfunction is intermittent
After the codes are cleared, test drive the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
Proceed by obtaining the diesel particulate filter pressure to voltage conversion data and diesel particulate filter pressure system wiring schematic or connector views for your vehicle
- Place the digital volt/ohmmeter + lead on the sensor reference voltage wire and the - lead on the ground wire
- Place the digital volt/ohmmeter in such a position as to be able to read it from the driver's seat
- Start the vehicle and observe the digital volt/ohmmeter while revving the engine
- If the diesel particulate filter pressure increases as RPMs increase, the problem may be intermittent
- If this is the case, clear the code and test drive
- If the diesel particulate filter pressure fails to change with varying RPM levels, suspect a clogged diesel particulate filter pressure tube and/or sensor
- Remove these two items and clean them thoroughly
- Reinstall, reset the code, and test drive the vehicle
If the diesel particulate filter pressure tube and sensor are not clogged, check for a voltage and ground signal at the diesel particulate filter pressure sensor
- If either signal is open, use the digital volt/ohmmeter to test the diesel particulate filter pressure sensor and the individual circuits
- Disconnect the PCM connector prior to checking circuit resistance levels
- Repair open or shorted wiring, components, or connectors as required.
If the electrical circuits and the exhaust back pressure vent control solenoid comply with the manufacturer's specifications, suspect a defective PCM
- Keep in mind that PCM failure is rare and replacement will require reprogramming.