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Author Topic: EGR/EVP Codes 31/32/33/34/35 Troubleshooting  (Read 22576 times)
El Hombre
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« on: April 22, 2011, 03:20:35 pm »

EGR/EVP Codes 31/32/33/34/35 Troubleshooting

Codes Definitions:

31 - EGR Valve Position/Pressure Feedback EGR Circuit Below Minimum Voltage. 0.24 volts (O,CM,R)
32 - EGR Valve Position/Pressure Feedback EGR Voltage Below Closed Voltage. 0.24 volts (O,CM,R)
33 - EGR Valve Opening Not Detected (CM,R)
34 - EGR Valve Position/Pressure Feedback EGR Voltage Above Closed Limit (O,R), PFE or EVP circuit has intermittently failed above the closed limit of 0.67 volts (CM)
35 - EGR Valve Position/EGR Pressure Feedback EGR Circuit Above Maximum Voltage of 4.81 volts (O,R), PFE or EVP circuit has intermittently failed above the maximum limit of 4.81 volts (CM)

EGR valve and EGR Valve Position (EVP) Sensor

EGR Vacuum Regulator (EVR) Valve


Background Information an Previous Misconceptions

EGR systems are a mechanical way used to re-inject inert exhaust gases to the intake as a mechanism to lower combustion temperature at the chamber. It is used to lower the emission of NOx (Nitrogen Oxide) gases to the atmosphere by reducing the combustion process temperature.

  • Engine idle control. The EEC uses the 6 MPH value threshold to activate idle dashpot strategy and prevent engine stalls coming to a stop and tip in when shifting.
  • VSS input is also an engine load determiner along with other inputs (TPS, MAF, etc).
  • Having a code 29 logged in the system can cause engine stalls in configurations with a manual transmission.
  • Its cruise control use has not changed.
  • Since VSS input is used to activate the dashpot function, it is normal to have a higher idle when transmission is shifted to neutral and the vehicle is above the 6 MPH threshold value. This is NOT an idle control problem (as it is erroneously tagged)... the system was designed to work as explained.

Tools Required: (in addition to the generic tools)

  • Digital VOM or DMM
  • Wiring diagrams for your year Mustang
  • Vacuum diagram for your year Mustang

Testing Procedure:

1. Disconnect the EVP sensor connector. With the ignition ON and the engine OFF, measure the voltage between VREF and SIGRTN terminals of the EVP sensor harness connector. If the voltage is 4vdc-6vdc, the power circuits to the sensor are OK...goto 2.....NOK?...check VREF to battery ground....OK?...SIGRTN wire needs to checked for open condition....NOK?...goto 3.

2. Reconnect the EVP sensor. With the ignition ON and the engine OFF, measure the voltage between EVP sensor terminals EVP and SIG RTN. If the voltage reading is between .25vdc - .67vdc the sensor is okay....goto 4......NOK?...replace EVP sensor.

3. Check VREF voltage at alternate sensor (TPS or BP), sensor disconnected, Ign On, voltage should be between 4vdc-6vdc....OK?...trace EVP VREF wire for open condition in harness....NOK?...rerun KOEO and confirm failure code presence of sensor used for this test.

4. Ign Off, ECM and EVP sensor disconnected, check continuity of the EVP signal wire pin from the sensor connector to pin 27 at the ECM connector, resistance reading should be less/equal to 5 ohms....NOK?...trace EVP signal wire for an open condition and repair.....OK?.....bad ECM.

Code 33 means the EVP sensor output voltage did not change when ECM expected EVP to register valve opening via an EVP signal voltage increase. Check connection and condition of vacuum line from EGR Valve Regulator (EVR) to EGR valve, repair/replace if necessary. Further testing for code 33 is explained in the "EVR Code 84 Troubleshooting" thread.

Quick Tips for Specific Codes:

Code 31:
  • Disconnect EVP sensor and install jumper wire between the EVP and VREF terminals.... run a KOEO.
  • Code 31 should not show as an OD type code and should be replaced by code 34 and/or 35.

Code 34 and or 35:
  • Disconnect EVP sensor...... run a KOEO.
  • Code 34/35 should not show as an OD type code and should be replaced by code 31.

Hope this helps someone....



'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2

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