EGR position sensor test - code 31

[swingjunkie]

1985 2.3L EFI
Engine code 31 - EGR Valve Control Sensor Fault

I just replaced the EGR valve in an attempt to clear this code. I did not replace the EGR position sensor. This was a fail, I still have the code 31.

I guess my next step would be to replace the sensor but I'd like to be sure I don't have some other issue first. Is there a way to test the EGR position sensor/circuit?

Thanks in Advance
Carl

 

[RonD]

EGR(EVR) systems have 3 parts
1. EGR Valve, opens and closes allowing exhaust gases into the intake to cool cylinders, this is vacuum operated.

2. EGR sensor(called DPFE on later years), detects if EGR valve is opening and how far.

3. EGR solenoid or modulator, 12volt solenoid controlled by the computer, this controls the vacuum going to the EGR valve, follow EGR vacuum hose to this solenoid, it will have another vacuum hose going to intake.

(4.) vacuum canister, found on some older EGR systems, it would store vacuum pressure for EGR system, when you open throttle quickly vacuum in intake will drop so EGR valve could close when it should be opening.

Since EGR system is only used to cool down cylinders when engine is under load(lowers NOx emissions) the computer uses RPM, MAP(or MAF) and throttle position data to decided when to open EGR valve.

Code 31 is usually bad wire connection(EGR sensor), cracked or loose vacuum line or bad EGR sensor.
It could be a bad section in computer circuit board or computer reference voltage, but there would be other codes as well if this was the case.

You will have prevented future problems by replacing EGR Valve, they do wear out.

Make sure to clear the codes after repairs, if you unhook the negative battery cable while working on a vehicle, a good safety habit, if cable is unhooked for at least 5 minutes this will also reset/clear computer codes for a fresh restart.

 

[swingjunkie]

Thanks Ron,

What I was thinking of is #2) EGR position sensor. It seems it should have a valid range of voltage input/output to/from the computer. So if anyone knows what a valid range of input/output values is at the connector, that might help me check the wiring/circuit in/out conditions.

My 1985 2.3L EFI does not have a separate solenoid or modulator for the EGR. EGR vacuum line comes directly off the vacuum tree on top of the intake manifold. It seems to me, on this early EFI engine, the control system is relying only on the vacuum level to control the EGR position.

The OBD reader does not show any stored codes for this engine. My code 31 shows up only when I run the KOER test.

Thanks
Carl

 

[RonD]

Then it has been hooked up incorrectly, but since engine idles OK I would say you may have followed the wrong hose.
If EGR valve had vacuum hose directly to intake then engine wouldn't start very well, and die if it did.

Vacuum diagram here for 1985 2.3l: http://www.autozone.com/repairguide...DIAGRAMS/VACUUM-DIAGRAMS/_/P-0900c15280077fce

scroll down to: Fig. 7: Vacuum hose routing-1985 2.3L engines

SOL V is a vacuum solenoid controlled by computer.
VRESER is a vacuum reservoir(can)
VREBER is a misprint, lol, should be VRESER

Computer sends EGR sensor 5volts, return voltage should be .3 to 3v I believe

 

[swingjunkie]

RonD,

You are correct and I am wrong. Thanks for pointing out the vacuum hose routing diagram. I have the vehicle diagram for my truck still intact on the truck. Here is a picture (age spots and all).
https://www.dropbox.com/s/jtpio7lt3gq3lnh/1985 Ranger 2.3L EFI vacuum diagram.jpg?dl=0

Mine does not show the VRESER between the EGR solenoid and the intake manifold vacuum tree, but mine is connected as shown. I added a couple of lines not shown on the original.

Is there any way to test the Vaccum resevoir? Im curious whats inside this thing? Nothing?

Here are a couple of other pictures of the vacuum hose routing.
https://www.dropbox.com/sh/x5wjrls972gsyo1/AADlC43_q1ihzyjA4oayE7Ewa?dl=0

I did test the EGR valve position sensor.There were three wires connected to the plug
Orange/Yellow - Power
Black/White - Ground
Brown/Green - Signal

With Key On Engine Off (KOEO) I had 5.04 on Power and the Signal ramped up from 0.07 (open) to 4.74 (closed). I tested this with the sensor disconnected from the EGR and simply depressed the plunger to see how the voltage output varied. I can't say this is the correct voltage only that it seems to vary as expected if the EGR valve is being actuated.

Could the sensor code 31 be caused by a fault in one of the EGR solenoids? How would I test that.
In retesting tonight I also got a code 34 (EVAP control sensor below min voltage). For full disclosure I also have code 41, HEGO. I had hoped to resolve the EGR issue before installing the new O2 sensor.

 

[RonD]

I believe the lowest voltage would be above .30v, .07v is no voltage, so I would say sensor is bad.
Code 31 and 34 would be correct if your low voltage at sensor was .07v, that is out of range.
Vacuum solenoids are just 12v coils, apply 12volts and they open(click) like a relay.
If you suck on a vacuum line attached to solenoid it should hold pressure until you open it, yes a vacuum gauge and pump are the correct tools, but results of test would be the same, lol, solenoid is good or is bad.

Yes, a bad solenoid could cause those codes, computer can't test solenoid persay, it just sees the results from sensor when vacuum is applied.
Code 34 can be "EGR did not respond properly during test" which could indicate solenoid issue.

Yes, vacuum reservoir is basically an empty can, usually with a check valve on the vacuum source hose.
Power Brake Booster is a vacuum reservoir, with a check valve, if engine should stall while driving, so no more vacuum, power assist for brakes will still work for 3 or 4 pedal pushes because of the reserve in the power booster tank.

EGR system needs reservoir because EGR is used only when engine is under load, and when you open the throttle plate vacuum in intake drops to almost 0, until engine rpms can match throttle position, reservoir allows steady vacuum source under those conditions.

Code 41 is "System lean - System was lean for 15 seconds or more (no HO2S switching)"

That would fit if there is a vacuum leak in the EGR system or elsewhere, or even an exhaust manifold leak, or low fuel pressure.
It also means the O2 sensor is probably working.
Have you noticed a lack of power or pinging recently, those are signs of lean air/fuel mix.

The computer in your '85 uses a MAP sensor to determine fuel mix from tables in it's memory, if O2 sensor shows too much oxygen, lean,(it can't see fuel only oxygen), the computer adds more fuel to mix, opens injectors longer, it has a preset limit on how long it can hold open injectors for specific engine RPMs and load, when it gets to that limit it will set code 41 to let the driver know there is a problem.

It could be O2 sensor, they do wear out.
But more likely cause is a mechanical issue, i.e. vacuum leak, air leak in exhaust manifold, low fuel pressure.
A misfire dumps lots of oxygen into the exhaust, O2 sensor can't see the unburned fuel it just see the oxygen that wasn't used because of the misfire.

MAP sensor is on the fire wall, usually passenger side towards the middle, behind wiring harness.
It has a vacuum line coming from intake, check to make sure that vacuum line is air tight, no cracks or leaks.
MAP sensors rarely fail, not never, just rarely, but vacuum lines do crack and leak as they get older.

 

[swingjunkie]

Okay, so it sounds like my next step is to replace the EGR position sensor and see if that clears codes 31 and 34. Seems like I should get this one cleared up before pursuing the code 41 (HO2S) issue.

The truck has good power, no pinging. Static fuel pressure reads 38 psi (FPR disconnected at idle). Fuel pressure holds at 30 PSI (FPR connected) at idle or under load.

I do here the EGR solenoids clicking as I open up the throttle, so for now I will assume they are working. I did inspect the vacuum connections at the EGR solenoids and the MAP sensor. All of the vacuum lines on this engine are tight and in good condition, so I don't suspect a leak.

I'll post a follow up after replacing the EGR position sensor.

 

[kimcrwbr1]

Did you erase both the memory and reset the ecm? Run the KOEO test and when it starts sending codes end the test that will erase the memory, then disconnect the neg post on the battery for 1/2 hour to reset the computer values. Then start it and run it for at least 20 minutes at medium speeds and while the engine is still hot run the codes again. You must reset the computer and erase the memory after each repair wether you clean or replace a sensor and then run the engine for 20 minutes to confirm the repair. Never run the engine with a component disconnected. To check if the EGR is working while the engine is ideling apply manifold vacuum to the egr and the engine should stall.

 

[swingjunkie]

kimcrwbr1,

Thanks for that info. I will be sure to do this next go round.

I picked up a new EGR position sensor, and before installing it I decided to plug it in and see what I got for an output (KOEO). My results from the previous post, showed 0 - 4.75 volts out as I pushed the plunger in.

On the new unit I got nothing. No response on the signal out, as I pushed the plunger in. This caused me to suspect a bad ground at the connector. I used a piercing probe on the ground wire (Brown/Green) to test this and I have an open circuit between battery negative and this wire.

Can anyone verify the Brown/Green wire on this connector is the ground? And does anyone have a pointer to a wiring diargam so I can trace this ground back?

Thanks
Carl

 

[kimcrwbr1]

http://www.therangerstation.com/tec...les/Diagram_ElectronicEngControls2_3_3of3.JPG
Not sure if this is for your motor but the concept is the same I believe. The computer provides around 5 volts to the senser

 

[RonD]

Pin 26 on EEC(PCM) is the 5v from computer, Brown/white stripe wire
Brown/light green stripe is sensor voltage(return) to EEC(PCM)
Gray/red stripe is the Ground

 

[kimcrwbr1]

My book shows black/white stripe is ground from the computer test for ground to the throttle position senser if it is good you need to find the break in the wire from the computer pin 46 to the EVP.

 

[swingjunkie]

Okay, It sounds like there is not a clear standard for the wiring colors to the EGR. Mine is different than the reference diagram which is on this site, and from RonDs machine. My power, signal, and ground are all fine I had confused myself on which was signal and which was ground. I corrected the wire color in my earlier post.

Heres my machine
OR/Y = 5 v power
BL/W = ground
BR/G = signal out

With KOEO the old sensor reads .07 - 4.74V from open to fully closed. This was me depressing the plunger manually and watching the signal out. With the sensor setting in place on the EGR valve my minimum signal was still 0.07V. Which RonD indicates is out of range (should be 0.30 or more).

Testing the same way with the new sensor it reads 0.10 - 5.01 volts from open to fully closed. With the sensor setting in place on the EGR valve my minimum signal is now 0.54V. So this is above the minumum threshold.

So I conclude that my old sensor was indeed faulty and needed replaced.

So to answer my original question, you can test the signal out of the EGR with the EGR sensor in place by
1) Determining which wire is signal, power, and ground on the sensor
2) With KOEO verify you have 5V on power, and continuity from the ground to battery negative
3) Measure the signal out and ensure this is above the minimum (0.3V)
4) Start the engine and monitor signal out as you rev the engine. You should see the signal increase with RPM (not sure what max signal out is?)

So all that said I I started the thing up, and I no longer have the code 31, but I still have a code 34. Arrghhh!

 

[RonD]

Good work
Nice write up

I would assume from the test that the travel of the sensor is limited when attached to EGR Valve which brings the minimum voltage up above .30v

I believe Code 34 means the RPMs did not drop when computer opened EGR valve during test.

So probably not a sensor issue any longer unless it's the distributor sensor(tach) and engine wouldn't start if that were the case.

You could try clearing codes and retest.

This PDF describes Fords two solenoid and single solenoid EGR systems, not sure which one you have: http://www.tomco-inc.com/Tech_Tips/ttt31.pdf

I would also run your own test, put a vacuum line in EGR valve and suck on it with engine idling, RPMs should drop as exhaust gases enter intake.

 

[swingjunkie]

RonD,

Yes, the sensor seems to respond with +0.3 V when in place on the EGR valve. Indicating that the plunger on the EGR position sensor is depressed.


I will clear the codes and retest. My previous test was wth the vehicle stationary as I also am working on the braking system. Thanks for the link to the solenoid systems. Mine is a dual solenoid system; August 1985 EEC-IV EFI system. I will also try the vaccum test. Any idea on how much vacuum should be applied? What is normal vaccum at idle?