CODE: 31 (KOEO) - EVP circuit below minimum voltage. Vref (5 volt reference voltage supplied by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or MAP sensor located on the firewall near the center of the car. Use the black/white wire for the ground for the DVM.
With the sensor removed from the EGR and still connected, press the plunger and watch the voltage change on the brown/lt green wire. Pull the passenger side kick panel and measure the voltage at the computer. You will need to remove the plastic cover over the wires and probe them from the backside. A safety pin may prove very useful for this task. Use pin 27, EVR input (brown/lt green wire) and pin 46, signal ground (black/white wire) to measure the voltage. The orange/white wire is Vref and should always be 5 volts -/+ .25 volt. Be sure to measure Vref at the EGR sensor to rule out any broken wires or bad connections.
Measuring the voltage at the computer helps you spot broken wiring and intermittent connections. With the EGR sensor removed from the its mounting place, leave the wiring connector plugged into the EGR. Then try wiggling the EGR sensor and pigtail while checking the voltage. This will help find any wiring breaks or bad connections. You may need a helper to hold the voltmeter or wiggle the wires.
Code 32 – EGR voltage below closed limit. Vref (5 volt reference voltage supplied by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or MAP sensor located on the firewall near the center of the car. Use the black/white wire for the ground for the DVM.
Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other. Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending on the sensor. The center connection of the variable resistor is the slider that moves in response to the amount of vacuum applied. The slider has some minimum value of resistance greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish between a properly functioning sensor and one that had a broken wire or bad connection. The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at rest with no vacuum applied.
As vacuum is applied, the voltage on the slider increases (EVP). As the voltage increases, the computer knows the how much the EGR valve is opened and how much exhaust gas is being recirculated. It uses the load table to calculate the amount of exhaust gas required depending on RPM, Mass Air Flow, ACT, ECT & TPS. It then sends a signal to the Electronic Vacuum Regulator to hold, increase or decrease the vacuum being applied to the EGR valve.
Theory class is over now, let’s spin up our propeller head beanies and get with it… Go Gadget, Go…
Measure the resistance of the EGR sensor between the two end pins. You should see between 3500 to 5500 Ohms. With the sensor removed, measure the resistance again while pressing on the plunger. You should see the resistance drop from its high value to a low reading of 200-700 ohms depending on the sensor. No resistance readings, or values way out of range, the sensor is bad.
If the Orange white wire has Vref, (5 volts =/-.25 volt) then you have some wiring problems because the computer isn’t seeing the minimum voltage on the EVR pin. Ohm the wiring back to the computer. Check for resistance between the brown/lt green wire on the EGR sensor and pin 27 on the computer: you should have less than 1 ohm. Repeat the process for the orange/white wire and pin 26. Do it again between the black/white wire and pin 46. In no case should you have more than 1 ohm. Remember that resistance checks are always done with the power off the circuit.
Voltage and resistance checks are good: Here’s an EGR test procedure I copied from cjones
EGR test procedure
to check the EGR valve:
bring the engine to normal temp.
connect a vacuum pump to the EGR Valve or
see the EGR test jig drawing below. Connnect the test jig or to directly to manifold vacuum.
Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).
apply 5in vacuum to the valve.
Using the test jig, use your finger to vary the vacuum
if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.
if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.
if engine stumbled,
connect EGR test jig to the hose coming off of the EGR Valve.
Use your finger to cap the open port on the vacuum tee.
snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
did the vacuum gauge show about 2-5 in vacuum?
if not the EVR has failed
EGR test jig
t.
If the test procedure fails to provide proper vacuum, check vacuum feed lines for cracks & damage. If the vacuum lines are good, check the electrical wiring to the EVR. If the EVR electrical wiring is good, look for 12 volts on the red wire for the EVR. If the 12 volts is good, look for a varying voltage on the dark green wire on the EVR. Case of last resort, replace the EVR and then the computer
Code 33 - Insufficient EGR flow detected.
Look for vacuum leaks, cracked vacuum lines, failed EGR vacuum regulator. Check to see if you have 10” of vacuum at the EGR vacuum connection coming from the intake manifold. Look for electrical signal at the vacuum regulator solenoid valves located on the rear of the passenger side wheel well. Using a test light across the electrical connector, it should flicker as the electrical signal flickers. Remember that the computer does not source any power, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.
Check for resistance between the brown/lt green wire on the EGR sensor and pin 27 on the computer: you should have less than 1.5 ohm.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif
EGR test procedure courtesy of cjones
to check the EGR valve:
bring the engine to normal temp.
connect a vacuum pump to the EGR Valve or
see the EGR test jig drawing below. Connnect the test jig or to directly to manifold vacuum.
Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).
apply 5in vacuum to the valve.
Using the test jig, use your finger to vary the vacuum
if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.
if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.
if engine stumbled,
connect EGR test jig to the hose coming off of the EGR Valve.
Use your finger to cap the open port on the vacuum tee.
snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
did the vacuum gauge show about 2-5 in vacuum?
if not the EVR has failed
EGR test jig
The operation of the EGR vacuum regulator can be checked by using a test light applied across the wiring connector. Jumper the computer into self test mode and turn the key on but do not start the engine. You will hear all the actuators (including the EVR vacuum regulator) cycle. Watch for the light to flicker: that means the computer has signaled the EGR vacuum regulator successfully.
The codes 31 & 32 at almost the same time suggest wiring problems or bad connections at the EGR sensor connector. Check closely for broken wires and loose connections. Look along the length of the EGR sensor connector pigtal for damage or evidence of cuts or broken wiring. Clean the connector pins with a Q tip and some non-flammable brake parts or electrical contact cleaner.
The 33 code will probably go away once you have the 31 & 32 codes fixed.
