Exhaust Gas Recirculation "A" Control Circuit Low
The PCM has detected a problem with the rate of flow of the exhaust gas recirculation (EGR) system. A trouble code has been stored and a malfunction indicator lamp has been illuminated. Some vehicle models require multiple drive cycles for a malfunction indicator lamp to be illuminated.
Code Set Parameters
If the PCM does not detect the desired degree of change in manifold air pressure, when the EGR valve is activated, a code will be stored and a malfunction indicator lamp will be illuminated. Some models require multiple drive cycles to activate the service engine soon lamp and others illuminate on the initial failure. Some automakers use an EGR position sensor to monitor the EGR vales itself, and then the PCM calculates the desired EGR flow according to the percentage that the valve is opened at any given moment. If the manifold air pressure fails to coincide with the PCM calculations, a code will be stored and a service engine lamp illuminated. Fords typically utilize a delta pressure feedback EGR (DPFE) sensor to measure manifold air pressure and exhaust feedback. When these DPFE readings do not fall within manufacturer’s specifications a code is stored and a service engine lamp is illuminated.
There will likely be no symptoms present when this code is presented. A code will be stored and a service engine soon lamp will be illuminated, although it may take multiple drive cycles.
The most common causes of this code are clogged EGR passages and clogged DPFE sensor passages. You may also suspect a faulty EGR sensor, MAP sensor, faulty EGR valve, faulty EGR control solenoid, a broken vacuum line, or faulty electrical wiring (or connectors) as possible causes.
The most common misdiagnosis comes from those who see the phrase “EGR valve” and automatically replace an expensive EGR valve. The EGR valve is faulty much less frequently than other components or circuitry.
- EGR valve systems in passenger vehicles can be basically categorized by two designs
- The first (and most common) type is controlled by engine vacuum
- While there are several sub-categories to consider when perusing the vacuum operated EGR, all are activated (opened) using engine vacuum and a valve with a strong vacuum diaphragm
- The typical EGR system used in OBD-II equipped vehicles is controlled by the PCM using electrical solenoids or servos which are opened, to allow engine vacuum, and closed to restrict vacuum to the EGR valve
- Some models are equipped with multiple control servos used in sequence
- Engine sensor inputs like vehicle speed, throttle position, and RPM level are taken into account before these solenoids are activated by the PCM
- The valve is opened using engine vacuum (and an integrated diaphragm) and it is closed with spring pressure.
The second type of EGR valve system utilizes an electrically controlled valve
- In this system the valve itself is attached to the electrical solenoids or servos which open (and close) it using small electrical motors
- The PCM uses varying degrees of voltage to open the EGR valve to the desired amount
The PCM uses input data received from various engine drivability sensors to calculate both the desired amount of EGR flow and the actual amount of EGR flow
- Inputs from the throttle position sensor, vehicle speed sensor, the mass air flow sensor, and the oxygen sensors help the PCM to calculate the desired flow rate of the EGR system and adjust the valve accordingly
- The manifold air pressure sensor, barometric pressure sensor, and the delta pressure feedback EGR sensor (if equipped) aid the PCM in determining whether or not the EGR flow is correct
- In this case, EGR flow pertains to the flow of exhaust gases entering the intake manifold area, instead of gases that flow through the actual EGR valve
- Some manufacturers use an EGR position sensor to monitor the EGR pendulum position
- EGR flow is estimated from the position of the pendulum in the EGR valve
- Other automakers use the sensors mentioned above (MAP and BMP) to monitor changes between “EGR ON” and “EGR OFF” conditions
- These changes are recognized as changes in manifold air pressure, or vacuum
- Still others employ a delta pressure feedback EGR sensor and a specially designed exhaust tube to monitor both exhaust pressure feedback and changes in manifold air pressure, when the EGR valve is activated.
A suitable scanner and a digital volt/ohmmeter will be essential in performing a successful diagnosis of this code.
Begin with a visual inspection of all wiring and connectors
- Do not forget the vacuum lines and hoses
- 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
Using the scanner, in test drive mode, monitor EGR function and compare your findings with manufacturer’s specifications to determine if you have a hard fault or an intermittent condition
- If the condition is intermittent, suspect loose, corroded, or burnt wiring or connectors at the EGR valve, EGR control solenoids, or EGR and DPFE sensor
- A sticking EGR valve may also cause an intermittent failure
- Performing a wiggle test can help to determine where the malfunction lies
If no change in manifold air pressure is detected, when the PCM opens the EGR valve, disconnect the vacuum line from the EGR
- Carefully connect the hand held vacuum pump directly to the EGR
- Start the engine and run at idle
- Slowly apply vacuum to the EGR valve by pumping the hand held pump
- Observe EGR operation
- If the EGR opens and the engine does not stall, then the EGR passages are clogged and must be cleared
- Over time (and usually with a lot of mileage) carbon is formed inside of the engine
- This carbon can accumulate on the walls of the EGR passages and eventually restrict or totally block them
- Remove the EGR valve and locate the other end of the passage
- Some EGR passages exit just inside of the throttle body, others dump into the center of the intake manifold, and others use a single tube underneath the intake with a small hole for each cylinder
- If the EGR fails to operate under vacuum pressure, replace the EGR valve
- If the EGR valve opens and the engine stalls, check for vacuum to the EGR control solenoid
- If vacuum is present on the input side of the EGR solenoid, then disconnect the output vacuum line and activate the EGR system using the scanner
- Once the EGR system is activated, a small “tick” should be heard from the solenoid and there should vacuum should be present on the output side
- If no vacuum is present on the output side of the EGR solenoid, after it has been activated by the PCM, test for a voltage and ground signal at the EGR control solenoid connector
- Most EGR control solenoids use switched voltage with a ground pulse from the PCM completing the circuit and opening the solenoid
- Once the ground pulse is discontinued by the PCM, the solenoid closes and vacuum is restricted
- If no voltage or ground signals are present at the EGR control solenoid connector, unplug the PCM connector and check continuity (with the digital volt/ohmmeter) in the affected circuit
- Repair open or shorted wiring and connectors as necessary and recheck
If you are diagnosing an EGR system that uses an electrical or linear EGR valve, use the scanner to activate the EGR while the engine is idling
- If the engine fails to stall, unbolt the EGR from the engine, flip it upside down, and check for operation (some models will require that you ground the EGR valve to the engine)
- If the EGR valve fails to operate replace it, reset the code and retest
- If it operates, remove the EGR valve from the engine and crank the engine
- If the engine idles normally, then you have clogged EGR passages
- With the EGR removed, the engine should not idle normally (if at all)
- There should be a sound that resembles a major vacuum leak
- This information can help after you have cleared the EGR passages using a suitable tool and some type of manufacturer approved chemical agent
- If the engine stalls and the EGR is operating, test the EGR electrical connector for a voltage signal from the PCM
- Some linear EGR valves utilize multiple integrated servos for activation
- Follow the manufacturer’s specifications for EGR operating voltage and compare them with your findings
- If your voltage readings fail to coincide with those of the manufacturer, then unplug the PCM connector and test all wiring and connectors for proper resistance and continuity
- Repair open or shorted wiring and connectors as necessary, reset the code and retest