code 31...check resistance

[2543arvin]

alright got a code 31 and its been persistent for the last couple of days so I checked the afm today and it read 1030 ohms. The tsrm states that it should be between 2000 and 3000 for 68' temp. Its about 75 degrees here today, and I didnt think that it would make that much difference. So is replacing the afm a requirement at this point or do I have other options? Im saving for the maftpro, but Im worried that this could be hurting my engine at the time....my car already died twice today....anyway just seeking guidance from the supramania society.

Thanks for the help guys...

 

[Nick M]

Don't replace it until you can condemn it. That is best done on the frequency scale of your DVOM-digital volt and ohm meter, or more commonly the multimeter.

The ECU looks for that hertz sigal. Also as JJ said, the ECU doesn't give a shit about ohms.

Do you know how to check the frequency output?

 

[2543arvin]

nope, but I have a multimeter, thats how I checked the ohms....


could you explain?

Thanks

 

[2543arvin]

Can anybody help?

 

[Nick M]

Hey, if you can't wait that long, you can always go to Toyota.

First you need the factory EWD for your year. That will show you the signal wire to the ECU. Your car does not need to be running. But it can be checked either way. Measure the signal wire on hertz.

And check with Jetjock on parameters, because I don't know of the top of my head.

 

[2543arvin]

Hey, if you can't wait that long, you can always go to Toyota.

First you need the factory EWD for your year. That will show you the signal wire to the ECU. Your car does not need to be running. But it can be checked either way. Measure the signal wire on hertz.

And check with Jetjock on parameters, because I don't know of the top of my head.

Sorry, I didnt mean to sound rude, its just that Im afraid that I may be doing more damage to my car, and I cant have it out of commission very long(its my dd).

Okay....Ill check for the signal wire, but what do I need to test the frequency? What type of tool?


Also, even though I need to check the frequency, if the resistance is bad, shouldnt that mean that I need to replace my afm? I got that info out of the tsrm, is the only reason I ask.

Thanks Nick

 

[2543arvin]

Okay done a little searching and found a thread similar.
http://www.supramania.com/forums/showthread.php?t=45750&page=2&highlight=code+31

In this thread JetJock says to test the voltage on the connector from the wiring harness, I did that and on pin 3, I got 5.01 vdc and on pin 4, I got 5.02 vdc. Im not sure what the voltage should be but they are very close.....

Im so confused...:3d_frown:

 

[jetjock]

alright got a code 31 and its been persistent for the last couple of days so I checked the afm today and it read 1030 ohms. The tsrm states that it should be between 2000 and 3000 for 68' temp.

It'd serve you better to measure the part of the AFM that actually produces a code 31 and not the other part.

 

[2543arvin]

Okay done a little searching and found a thread similar.
http://www.supramania.com/forums/showthread.php?t=45750&page=2&highlight=code+31

In this thread JetJock says to test the voltage on the connector from the wiring harness, I did that and on pin 3, I got 5.01 vdc and on pin 4, I got 5.02 vdc. Im not sure what the voltage should be but they are very close.....

Im so confused...:3d_frown:

Did I measure the wrong thing? Im not sure what Im looking for as far as resistance, voltage, frequency(which I dont know how to test) or what....

 

[jetjock]

The AFM electronics has two sensors inside. One measures air flow and the other measures temperature. These two sensors are electrically and mechanically independent of each other. They also have their own codes. The part of the TSRM that refers to changing resistance with temperature involves the temperature sensor. It's not capable of causing a code 31. That code is associated with the air flow sensor. In other words the AFM has 5 wires. Two are for the temp sensor and three are for the air flow sensor. Depending on what code you're getting you need think of these wires as being connected to two separate devices because they are.

While measuring resistance works OK for the temp sensor it's a crap shoot doing it for the air flow sensor. This is because resistance can't measure the condition of the vibrating mirror which makes the air flow signal. That's why it's best to measure frequency of the KS signal and not resistance when dealing with code 31.

If your meter can't measure frequency use voltage. Set the meter to as close to a 5 volt range as it has and while looking at Ks (referenced to ground) raise the engine from idle and see if it changes. If so the Ks signal is probably good. That said it doesn't mean it's reaching the ECU.

Bottom line: The ECU will set code 31 if it sees a voltage at the KS input below 100 millivolts or higher than 4.8 volts, depending on whether the KS line is shorted or open.

 

[2543arvin]

The AFM electronics has two sensors inside. One measures air flow and the other measures temperature. These two sensors are electrically and mechanically independent of each other. They also have their own codes. The part of the TSRM that refers to changing resistance with temperature involves the temperature sensor. It's not capable of causing a code 31. That code is associated with the air flow sensor. In other words the AFM has 5 wires. Two are for the temp sensor and three are for the air flow sensor. Depending on what code you're getting you need think of these wires as being connected to two separate devices because they are.

While measuring resistance works OK for the temp sensor it's a crap shoot doing it for the air flow sensor. This is because resistance can't measure the condition of the vibrating mirror which makes the air flow signal. That's why it's best to measure frequency of the KS signal and not resistance when dealing with code 31.

If your meter can't measure frequency use voltage. Set the meter to as close to a 5 volt range as it has and while looking at Ks (referenced to ground) raise the engine from idle and see if it changes. If so the Ks signal is probably good. That said it doesn't mean it's reaching the ECU.

Bottom line: The ECU will set code 31 if it sees a voltage at the KS input below 100 millivolts or higher than 4.8 volts, depending on whether the KS line is shorted or open.

Okay, I just tried to do what you asked me and I believe I am doing something wrong. Just to clear things up for me....

1. I dont have a 5 volt range on my DMM, I have 20, 2000m, and 200m. Which to use...Im not sure.
2. When measuring the KS signal, the engine needs to be running and the connector plugged into the AFM, right? So therefore I am pressing the tip of the multimeter through the wire....does this sound accurate?

Im sorry for bothering you with the same shit you deal with everyday by people like me....Ive read through most of your other posts on this topic and still seemed got lost, but thanks for your help jetjock!

 

[jetjock]

Edit: Sorry, having a bad day. Is it too much to ask people behave when traveling? It's not my fault shit happens. People need to relax. You'd think they'd understand it's either that or go to jail but no...

Either punch through the wire insulation with a pin/needle or back probe the connector. The engine should be running.

 

[Grimsta]

Bottom line: The ECU will set code 31 if it sees a voltage at the KS input below 100 millivolts or higher than 4.8 volts, depending on whether the KS line is shorted or open.

Ah, thats what i was looking for since our crappy ass TSRM's only give BS resistance checks. Solved my problem, AFM's bad. Yeah, i dropped it and though it might still function normally, lol

 

[Shytheed Dumas]

1. I dont have a 5 volt range on my DMM, I have 20, 2000m, and 200m. Which to use...Im not sure.

The "m" refers to millivolts, so you have indicated three ranges:

20 volts
2 volts (equals 2000 mV)
0.2 volts (equals 200 mV)

As you switch between ranges you will see the decimal point move accordingly on the screen. A range of 200 mV will be extremely sensitive, but worthless at 10 to 100 times the voltage range you are expected to be in, so you sacrifice sensitivity for the ability to handle your actual voltage. I have no idea if JJ expects the voltage to come close to 5 volts (which is to say exceeding 2 volts), so start with the 20 volt range which should be sensitive enough to make the working/not working determination he outlined anyway.

 

[jetjock]

^ Thank you.

Power to sensors is 5 volts and the normal range of "legitimate" signal return is from 100 mv to 4.8 vdc. This 5 volt level for power and signal one of the things that distinguishes a TCCS from conventional EFI.

The "crappy-ass" TSRM also shows how to check voltages. It's the best way to do things because when you measure voltage you're measuring the same type of variable the ECU uses. ECU diagnostics though, at least as it applies to analog signals, can only sense shorts or opens. It can't sense shifted signals. Fwiw that's generally true about new cars too.

 

[2543arvin]

Thanks for the input guys....I will report back tomorrow with measurements, today has just been one of those days:3d_frown:

 

[Grimsta]

Indeed, i hate resistance tests. But my manual has no voltage test for the AFM. I know how to check voltage, frequency, perform voltage drop tests, etc, but i couldn't find any specifications so my measurements were meaningless without a reference, but since you so kindly posted them up there, yeah its time for a new AFM

 

[Nick M]

I think he comes back with a loose connection. Seems to be common on this older car, or at least that is what I read. Same as the cam postion sensor.

 

[2543arvin]

UPDATE!!!

Okay today I checked the KS signal with it at idle and got 3.10 vdc and at 2k rpms it read 3.21 vdc, Im not sure what this means but maybe you guys can help me.


btw, I reset my ecu yesterday and this reading was with the ecu not throwing any codes....

 

[2543arvin]

I drove it until it threw a code this time and now the KS signal changed when it went from idle to 4krpm(couldnt hold it at 2k),


@idle- 4.80vdc

@4k rpm- 2.80 vdc

Im not sure whats goin on....