P042F – Exhaust Gas Recirculation “A” Control Stuck Closed

By Stephen Darby (Contact Me)
Last Updated 2019-06-18
ASE Master Tech

Table of Contents

1. What Does Code P042F Mean?
2. What are the common causes of code P042F?
3. What are the symptoms of code P042F?
4. How do you troubleshoot code P042F?
5. Codes Related to P042F
6. Get Help with P042F

What Does Code P042F Mean?

A stored code P042F simply means that the powertrain control module (PCM) has detected a malfunction in the exhaust gas recirculation (EGR) valve control system. This particular code indicates that the EGR valve appears (to the PCM) to be stuck in the closed position. This code is applicable to the linear (or step-down) EGR. Designation A applies to a particular position or stage of the control system.
Nitrogen oxide (NOx) is produced as a side effect of gasoline and diesel engine operation. As part of the modern automotive exhaust emission control system, the EGR is necessary to reduce harmful levels of NOx. As the name implies, the EGR system permits the engine to consume a portion of unburned fuel from the exhaust system at controlled intervals.

At the heart of the linear EGR system is an electronically controlled valve. This valve is opened (under certain circumstances) to allow exhaust to re-enter the engine intake.

Input signals from the throttle position sensor (TPS), vehicle speed sensor (VSS), and the crankshaft position sensor (CKP) are used by the PCM to determine when and to what degree the EGR valve should be opened or closed. The linear EGR valve opens in stages which are determined by the degree which the throttle is opened, how much load is placed on the engine, and how fast the vehicle is moving. Most vehicles equipped with a linear EGR system use data from the manifold air pressure (MAP) sensor and/or the differential pressure feedback EGR (DPFE) sensor to determine whether the EGR valve is in the desired position. Some older models have a pintle position sensor integrated within the EGR valve. The position of the EGR valve pintle is monitored by this sensor, which delivers data directly to the PCM. If the EGR valve is suspected of being stuck closed, a code P042F will be stored and a malfunction indicator lamp (MIL) may be illuminated. Most vehicles will require multiple ignition cycles (with a failure) before MIL illumination will occur.

What are the common causes of code P042F?

• Clogged EGR passages
• EGR control solenoid/valve is bad
• Open or shorted wiring/connectors in the EGR control circuit
• Defective EGR valve
• Faulty MAP/DPFE sensor
• Bad EGR valve position sensor
• PCM malfunction or PCM programming error

What are the symptoms of code P042F?

• Symptoms are rarely exhibited with this code
• Slightly diminished fuel efficiency

How do you troubleshoot code P042F?

A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of reliable vehicle information will be necessary to diagnose a code P042F.

Searching technical service bulletins (TSB) that replicate the code stored, vehicle (year, make, model, and engine), and symptoms exhibited could net a faster diagnosis. TSB information can be found in your vehicle information source.

Prior to clearing stored codes, use the scanner (connected to the vehicle diagnostic port) to retrieve all stored codes and pertinent freeze frame data. Write the information down (in case the code/s proves to be an intermittent one). Once codes are recorded, clear the codes and test drive the vehicle. One of two things will likely occur; the code will be restored or the PCM will enter readiness mode. If the code is intermittent the PCM may enter readiness mode. If this occurs, the condition which caused the P042F to be stored may need to worsen before an accurate diagnosis can be made. Continue with the diagnosis if the code is restored.

Use your vehicle information source to obtain connector face views, connector pinout charts, component locator charts, wiring diagrams, and diagnostic flow charts (pertaining to the code and vehicle in question). Perform a visual inspection of related wiring and connectors and repair or replace wiring that has been cut, burned, or damaged.

The DVOM may be used to test voltage and ground circuits at the EGR valve, engine sensors, or PCM. If no voltage is detected, check system relays and related fuses. Replace defective relays and/or blown (or otherwise defective) fuses as required. Test EGR valve and system components following manufacturer’s guidelines. If voltage and ground are not detected at the EGR component, test the corresponding circuit at the PCM connector. If no voltage is detected there, suspect an open circuit between the component in question and the PCM. If voltage is discovered there, suspect a defective PCM or a programming error.

Codes Related to P042F

• P0401 Exhaust EGR Flow Insufficient
• P0404 Exhaust Gas Recirculation Circuit Range/Performance
• P042E Exhaust Gas Recirculation A Control Stuck Open
• P0490 Exhaust Gas Recirculation A Control Circuit High

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