Technical Description of OBD-II Trouble Code
Exhaust Pressure Control Valve “B”
What is the meaning of this code?
This code is commonly found in diesel engines, specifically in certain Ford, Dodge, Mercedes, Nissan, and VW vehicles. It can also apply to trucks with diesel engines and dealer-installed exhaust brakes. The code refers to a valve placed in the exhaust stream after the exhaust manifold. This valve generates heat in the form of back pressure, which can assist in cold start warm-up and slow down the engine and vehicle by opposing cylinder pressure. This is particularly useful during towing operations.
The code specifically relates to the output circuit of the exhaust pressure control solenoid. It is considered an electrical circuit fault.
Troubleshooting steps may vary depending on the manufacturer, type of exhaust back pressure control, and wire colors of the control solenoid. Consult a vehicle-specific repair manual to identify the “B” valve in your particular case.
Symptoms of the Code
The symptoms of a P049F engine code may include:
Possible Causes of P049F
The typical causes for this code to set are:
Diagnostic and Repair Procedures
A good starting point is to search for a technical service bulletin (TSB) related to your specific vehicle. The vehicle manufacturer may have a PCM flash/reprogram to address this issue, so it is worth checking before proceeding.
Next, locate the “B” Exhaust Pressure Control Solenoid on your vehicle and visually inspect the connectors and wiring. Look for any signs of damage such as chafing, rubbing, bare wires, burn spots, or melted plastic. Disconnect the connectors and inspect the terminals for corrosion, burning, or unusual discoloration. Clean the terminals if necessary using electrical contact cleaner or rubbing alcohol. Apply dielectric silicone compound to the terminals for protection.
If you have a scan tool, clear the diagnostic trouble codes from memory and monitor if the code returns. If it does not, the issue was likely related to the connections.
If the code does return, further testing of the solenoid and its circuits is necessary. Typically, there are 2 wires connected to the Exhaust Pressure Control Solenoid. Use a Digital Volt Ohm Meter (DVOM) to check for open or shorted circuits. Replace the solenoid if it is faulty.
If the solenoid is functioning properly, use a DVOM to check for 12V on the solenoid power supply circuit. Ensure that the ignition is on. If there is no 12 volts or if there is 12 volts when the ignition is turned off, repair the wiring or consider a possible issue with the PCM.
Next, check for a good ground at the Exhaust Pressure Control Solenoid. Use a test light connected to a 12V battery positive terminal and touch the other end to the ground circuit of the solenoid. If the test light does not illuminate, there is a problem with the circuit. Wiggle the wiring harness of each sensor to check for intermittent connections if the test light flickers.
If all tests have been passed and the P049F code persists, it is likely that the Exhaust Pressure Control Solenoid has failed. However, the possibility of a failed PCM cannot be ruled out until the solenoid is replaced.
