obd1 code 31 - Toyota Nation Forum : Toyota Car and Truck Forums

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post #1 of 11 Old 03-08-2010, 07:16 PM Thread Starter
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obd1 code 31

I have a 1989 Toyota 4runner I just bought. It sat for about a year to a year and a half an dwas not started. I put a battery in it and 5 gal of gas and it started fairly easy. It is missing at an idle and really doesnt like you to accelerate. It has a check engine code of 31. It might be just my imagination but smells like rotton eggs or sulfer. I was thinking that the catalytic converter would be bad but I was wondering what would cause the engine code of 31. It is a 2.4 liter 4cyl 5 speed 4x4. Thanks
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post #2 of 11 Old 03-08-2010, 08:51 PM
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Code 31=Air flow meter, to see full codes see below also measure the voltages and reistances on ECU and compare with service manual to isolate problem.

About half of the ECU codes stored on the first & second generation EFI Toyotas don't show a constant blinking check engine light therefore you must pull the ECU codes to see if a fault is registered.

To pull the ECU codes:

All 1980-1995 and including 1995 EFI equipped vehicle allow you to find engine and related faults by pulling the ECU (computer) codes without the need for a handheld OBDII diagnosis scanner, the sites listed below have the fault codes needed to pull the codes and the instructions on how to do it:

http://autorepair.about.com/library/...bl-dtcs-36.htm
http://autorepair.about.com/library/...bl-dtcs-53.htm
http://autorepair.about.com/library/...bl-dtcs-71.htm
http://autorepair.about.com/library/...bl-dtcs-90.htm
http://www.autozone.com/az/cds/en_us...rInfoPages.htm
http://www.off-road.com/toyota/tech/codes/index.html
http://www.4crawler.com/4x4/CheapTri...CheckConnector
http://www.4crawler.com/4x4/CheapTri...osticcodes.gif
http://lcengineering.com/TechNotes/TechNote12.htm
http://lcengineering.com/TechNotes/TechNote13.htm
http://www.geocities.com/MotorCity/P...ct/Engine.html
http://www.mad-mechanic.com/toyota/t...tml#obtaincode
http://www.freewebs.com/th3duke/22RE-ECU.mht
http://www.troublecodes.net/Toyota
http://www.autoshop101.com/forms/h27.pdf
http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx
http://www.showmesome.info/hilux/inf...E/Page0096.htm
http://www.efisakh.narod.ru/at_toyota.htm (auto tranny codes)
http://www.usatransdoctor.com/foreigntoyota.htm
http://www.obd-codes.com/forums/viewforum.php?f=3

Pulling the ECU (EFI computer) codes is the first thing I do to diagnosis a problem thereafter I reset the ECU to see if the same problems show up and if so I then take voltage measurements at each ECU wire both with the engine running and not and compare with the factory service manual, I also close the ignition switch after a cold engine and also after a warm engine and compare the resistance values with the factory service manual. This technique will completely isolate your problem without having to do trial and error and it is the technique I use when repairing tv's, vcr's, home/car audio.

Sidney
E-mail:sidneybek(at)yahoo.com
Dartmouth,Nova Scotia
Canada
1995 Toyota 4-Runner,22R-E with 243 000 KM
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post #3 of 11 Old 03-08-2016, 10:12 PM
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Sidney, could you explain that last paragraph in more detail, please? I'm getting a 31 code (hesitation regardless of speed) and have replaced the AFM with 4 different units with no change in performance. Have also switched out the ECU - still no change!
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post #4 of 11 Old 03-08-2016, 10:33 PM
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It could mean the problem is with the wiring between the AFM and the ECU.

''Open circuit in Vc signal or short
circuit between Vs and E 2 when idle
contacts are closed.''

Check the wiring!

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post #5 of 11 Old 03-08-2016, 10:57 PM
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Thank you, Phil
I'm beginning to think there's a wiring problem - just wasn't sure where to look. Now all I have to do is figure out where those points are you referred to. There's an E2 on the AFM, ECU, and TPS, isn't there?
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post #6 of 11 Old 03-08-2016, 11:58 PM
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Yes of course, since E2 = ground.

The AFM and the TPS are simply fancy potentiometers. VC is the reference voltage sent by the ECU, E2 is the ground.



So for the AFM VC would be pin A, VS is W (the wiper) and E2 is B. Same thing for a TPS but in that case the wiper would be called VTA.

If the ECU sends a reference voltage (VC) of 5V for instance, the position of the wiper on the resistive material between VC and E2 will send back a voltage anywhere between 5 and 0V which the ECU will interpret as the position of the flap inside the AFM or the butterfly valve inside the throttle body.

If you disconnect VS the ECU will see 0V at the wiper. Same thing if you disconnect the wiper. If you disconnect E2 the potentiometer will stop acting as a voltage divider to become a variable resistor and it will send innaccurate infos to the ECU.

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Last edited by Phil_Bleach; 03-09-2016 at 12:07 AM.
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post #7 of 11 Old 03-09-2016, 06:23 PM
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Lost me. I'm somewhat mechanically inclined, but I'm not a mechanic. Sounds like I need to check continuity from some point on the ECU to some point on the AFM?
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post #8 of 11 Old 03-10-2016, 07:15 PM
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OK, I'm over my brain f*#t. Pulled the plug off the ECU and found an open between Vs and Vc....further testing found the Vs wire fine, and an open in the Vc wire. Good call, and thanks again, Phil!

Now, suggestions on a fix????
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post #9 of 11 Old 03-12-2016, 04:17 PM
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Darn! Not over my stupidity!! Was reading the ECU wiring diagram wrong. 156 Ohms across Vs - Vc measured at ECU plug...

Now, however, instead of getting a 31 code when I try to read the code it flashes rapidly constantly.....does that mean the system is normal??

Also seems to be running just fine now.

Last edited by ToyotaSlim; 03-12-2016 at 05:12 PM.
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post #10 of 11 Old 03-12-2016, 10:32 PM
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Quote:
Originally Posted by ToyotaSlim View Post
does that mean the system is normal??
Yep, all clear
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post #11 of 11 Old 03-13-2016, 12:22 AM
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Woo-hoo!!
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