Unlock Better Engine Performance with EVP Sensors

As an Amazon associate, we earn from qualifying purchases.

Purpose

The EGR Valve Position (EVP) Sensor is used on most Ford vehicles equipped with EEC-IV Electronic Engine Control systems to monitor the position of the EGR valve. The vehicle’s computer can tell when the valve is closed, when it's open and by how much.

From this, the computer uses this information to determine the correct exhaust recirculation flow rate to effectively reduce NOX emissions. The vehicle’s computer controls the EGR valve by actuating two vacuum solenoids; the EGR Control (EGRC) solenoid and the EGR Vent (EGRV) solenoid.

Location

The EVP sensor is mounted on top of the EGR valve, with the sensor’s potentiometer shaft resting on the EGR valve stem.

Operation

The EVP sensor is a linear potentiometer similar to the throttle position sensor. The resistance of the EVP sensor changes in proportion to the position of the EGR valve stem. When the EGR valve opens and closes, the EVP potentiometer shaft moves in an amount equal to the position of the EGR valve stem. When the EGR valve is closed, EVP sensor resistance is at its maximum.

As the EGR valve opens, EVP sensor resistance decreases until it reaches its minimum value when the EGR valve is fully open. When the EGR valve is fully closed, EVP sensor resistance should not exceed 5500 ohms. When the EGR valve is fully open, EVP sensor resistance should not be less than 100 ohms.

Drivability Symptoms

A malfunction in the EVP sensor or circuit will cause a faulty signal (or no signal) to be transmitted to the vehicle’s computer. In such a case, the vehicle’s computer cannot accurately determine the position of the EGR valve.

The computer will attempt to regulate the EGR valve based on other inputs (throttle position, manifold absolute pressure); however, EGR valve control will not be as accurate, and some drivability problems may occur.

The following symptoms may indicate a damaged or defective EVP sensor, or trouble in a related system:

• Hesitation during acceleration, rough idle and/or hard starting. These conditions may indicate a faulty EGR valve that has become stuck in the “open” position. This is generally caused by a buildup of carbon at the base of the valve. Cleaning carbon deposits from the valve will usually return the unit to serviceable condition.
  
• Audible pinging or knocking while accelerating or driving under load. Detonation, or knocking generally occurs when the EGR valve fails in the “closed” position. The loss of exhaust gas recirculation causes an increase in combustion temperatures, resulting in spark knock while acceleration or when driving under load. The problem may be caused by a defective EGR valve or as a result of loss of vacuum to the valve (caused by a vacuum leak, faulty vacuum solenoid, or electrical problem in one or both solenoid control circuits).
  

Testing and Troubleshooting

Problems with the EVP sensor itself can be caused by short or open circuits in the EVP sensor wiring. Damaged connector pins are generally the cause of these types of faults. Additionally, excessive wear may cause the EVP sensor to “stick”, resulting in an inaccurate signal output to the vehicle’s computer.

The EVP sensor and related circuits can be tested while installed on the vehicle using the following procedures.

EVP Sensor Operational Check

Use a digital ohmmeter and hand vacuum pump to verify proper operation of the EVP sensor, as follows:

• Set the ohmmeter to the 200K scale.
• Unplug the wiring harness from the EVP sensor connector.
• Connect one lead from the ohmmeter to the EVP sensor’s EVP SIG terminal; connect the other lead to the VREF terminal.
  
  Verify EVP sensor resistance is 5500 ohms maximum with the EGR valve fully “closed.”
  
• Disconnect the vacuum line from the EGR valve and connect a hand pump to the vacuum fitting.
• Observe the ohmmeter, and slowly apply vacuum to the EGR valve (DO NOT exceed 10psig).
  
  Verify EVP sensor resistance decreases gradually and smoothly as the EGR valve opens (as vacuum is applied).
  
  Verify EVP sensor resistance is 100 ohms minimum with the EGR valve fully “open.”
  
• Disconnect the hand pump and ohmmeter from the EGR valve and EVP sensor. Reconnect the vacuum line to the EGR valve vacuum fitting. Reconnect the wiring harness to the EVP sensor connector.

The following test results may indicate a defective EVP sensor:

• EVP sensor resistance at the EGR valve “closed” and/or “open” position is not within specified limits.
  
• Resistance during testing changes sharply, or not at all.
  
• Resistance increases as vacuum is applied to the EGR valve.
  

EVP Sensor Signal Voltage Check

Use a digital voltmeter to check for proper signal voltage to the EVP sensor.

• Set the digital voltmeter set to the 20V scale.
• Unplug the wiring harness from the EVP sensor connector.
• Turn the ignition on. DO NOT start the engine.
  
• Measure the voltage between the wiring harness VREF and SIG RTN terminals.
  
  Verify the voltage is 4 ~ 6 volts.
• Measure the voltage between the wiring harness VREF and EVP SIG terminals.
  
  Verify the voltage is 4 ~ 6 volts.
  
• Turn the ignition key off. Reconnect the wiring harness to the EVP sensor connector.

If the VREF to SIG RTN and/or VREF to EVP SIG voltage is not as specified, an electrical short or open in the wiring is likely. Use a suitable continuity tester to check wiring continuity. If no wiring faults can be found, the vehicle’s on-board computer may be defective.

Vacuum Check

If the EVP sensor, sensor wiring and the vehicle’s computer are found to be in good condition, use a vacuum gauge to monitor vacuum at the EGR valve with the engine running.

Vacuum should cycle on and off in less than two seconds at the EGR valve when the engine is at normal operating temperature and the throttle is opened and closed. Always follow the diagnostic procedures in the service manual for your vehicle to isolate the fault when the EVP sensor appears to be defective.

Repair/Replacement

The EVP sensor is a sealed unit. If you determine it is defective, it must be replaced. No repair or adjustment is possible.

Back to Blog Academy