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Error Code P049F is defined as Exhaust Pressure Control Valve B. This is a generic trouble code that applies to all diesel engines, including but not limited to Dodge, Ford, Mercedes Benz, Nissan, and Volkswagen vehicles. It also applies to diesel engine trucks and dealer installed exhaust brakes. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
To generate heat through back pressure in the exhaust, a valve is placed in the exhaust stream after the exhaust manifold. This used (or back pressure) is such a great during cold start warm up as it increases the cab heat and significantly reduces the amount of time to defrost the windshield. Also, this heat can be used to oppose cylinder pressure that comes from the engine cylinders outside the exhaust, which slows the engine downs, as well as the vehicle. This is particularly helpful during towing operations.
The PCM (powertrain control module, also known as ECM or engine control module in other vehicles makes) uses the measured exhaust back pressure (ambient) intake air temperature, engine oil temperature, and engine load to determine the desired exhaust back pressure.
Valve position is controlled by switching the output signal circuit to 12 volts inside the PCM. On/off time is modulated from 0 to 99 % dependent upon the exhaust back pressure desired.
Error code P049F happens when the output circuit to the exhaust pressure control solenoid is outside the specifications set by the manufacturer.
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:
- Lack of engine power
- Lack of engine braking
- Engine takes longer time to warm-up
Common causes for this code include:
- Open in the power supply circuit between the exhaust pressure control solenoid and the PCM
- Short to Power in the power supply circuit between the exhaust pressure control solenoid and the PCM (powertrain control module)
- Short to ground in the power supply circuit to the exhaust pressure control solenoid
- Defective Exhaust Pressure Control Solenoid
- Failed PCM (rare)
How to Check
Use the TSB (technical service bulletins) and look for the entry; match the vehicle, codes stored, and symptoms exhibited. Most manufacturers post updated solutions for errors like this, which makes this a good starting point for diagnosis.
Next, find the “B” Exhaust Pressure Control Solenoid of your vehicle and conduct a visual inspection of the connectors and wiring. Look for signs of damages, such as bare wires, burn spots, chafing, rubbing, or melted plastic.
Inspect the terminals (metal parts) by pulling the connectors apart inside the connectors, and look for signs of damage, such as burning, corrosion, or possibly green in color versus the normal metal color you are probably used to seeing.
Use an electrical contact cleaner to clean the terminals (if necessary) If you don’t have access to a special cleaner, then use a 91% rubbing alcohol, along with a light plastic bristle brush to clean the terminals thoroughly. Let them air dry, get some dielectric silicone compound and put somewhere the terminals come into contact.
Use a scan tool to retrieve all data stored in the vehicle. Reset the codes and see whether the code returns after a test drive.
If the code returns, then check the solenoid and all of its associated circuits. Usually, there are two types of wires at the Exhaust Pressure Control Solenoid. The first one disconnects the harness that goes to the Exhaust Pressure Control Solenoid.
Connect the DVOM into one terminal of the solenoid. Pay attention to the remaining meter to the other solenoid terminals. They must NOT be open or shorted.
Then, connect the remaining meter lead to the other solenoid terminal. It should not be open or shorted. Check for the specific resistance set by the manufacturer for your particular vehicle. If the solenoid is either open or shorted (infinite resistance or no resistance/0 ohms), then you have to replace the solenoid.
If everything seems to be fine, check if you can get 12V on the Exhaust Pressure Control Solenoid power supply circuit (Red lead to the solenoid power supply circuit, black lead to a good ground).Make sure the ignition is on. If you can’t get 12V to the solenoid, or if the, or if there’s 12V when the ignition is off, then you have to repair the wiring from the PCM, relay to the solenoid, or you may have a bad PCM.
Check whether there’s a good ground to the Exhaust Pressure Control Solenoid. Use a test light; connect one end to the 12V battery positive (red terminal) and use your fingers to touch the other end of the test light to the ground circuit going to the Exhaust Pressure Control Solenoid circuit ground. If the light doesn’t light up, then you have a circuit problem. If it lights up, then wiggle the wiring harness that goes to each sensor to see if the light flickers. If it does, then that means there’s an intermittent connection.
How to Fix
Common fixes for this code are:
- Repair or replacement of damaged wiring or connectors at the Exhaust Pressure Control Solenoid
- Solenoid replacement
- Repair or replacement of the wiring from the PCM
- Replace and update the PCM
If after doing the diagnosis and repairs the error code is still there, then you probably have a defective PCM.