Codes 31 & 52

[huntin5L]

Alright,


My car ran like like complete crap this morning and so I checked my codes and sure enough, codes 31 and 52 were logged. 31, which I believe is the afm, which I replaced a few months ago and has been serving me well and 52, which looks like the knock sensors. My question is how can this afm go bad already?? Also, 52 seems to be quite random, and I can go many months without getting a cel for it. So, what do I need to test the afm/knock sensors, multi-meter? and what should the specs be? By the way, once I cleared the codes the car seemed to run just fine, my assumption is that by erasing the codes takes the ecu out of whatever crappy mode it was running in. LMK

 

[GC89]

If you forgot to plug the the afm in and tried starting it it would throw the afm code and store it. If it was running ruff that alone could have tripped the knock sensor, so that is probably a symptom rather than part of the issue.

 

[huntin5L]

Good point, but I think it is plugged in, im going to check in a little bit.

 

[GC89]

It could have been from quite a while ago, the ecu stores codes until they are cleared. The two could be competely unrelated, what was the temp & weather like and how long had the car sat.

 

[huntin5L]

The car sat for a couple of days, it is cold, im in chicago. Yeah i know they store codes until they are cleared, i cleared them again this morning. I think it could be the afm causing this, I have seen the 52 randomly, though not very often.

 

[Quin]

Sounds like faulty wiring if it randomly happens. Have you done the knock sensor rewire?

 

[shaeff]

If it was running ruff that alone could have tripped the knock sensor, so that is probably a symptom rather than part of the issue.

uh, no. code 52 is unrelated to the AFM in every way. all it means is that there's a short somewhere in the wiring between the actual sensor(s), and the ECU. running rough has nothing to do with it.

hell, you could have rodknock on all six cylinders and STILL not get code 52.

 

[cuel]

* 7M-GTE) Open or short circuit in air flow meter signal.

Check the plug, and the wires there. Make sure the wires are seated correctly in the connector, and that all of the connectors are making good contact. Check that there aren't any wires with missing insulation touching each other. If there are any wires missing insulation, you need to fix them.

 

[jetjock]

What shaeff said, for what is probably the thousandth time.

There is only one thing that can cause code 52: The ECU isn't sampling normal ignition events. That's usually caused by a faulty knock sensor or a bad (open or shorted) signal path and on very rare occasions noise in the circuit. And fwiw 52 may seem random but it's not. I won't bore you with what they are but specific patterns of time, load, and rpm must occur before the MIL comes on.

Cuel is, as usual, dead on regarding the AFM code...

 

[cuel]

That's just because I pay attention to, and learn from, what the Experts post, each in they're own area of expertise.

I've learned more technical information here from reading after JJ, IJ, JDub, and others than in my usual day to day. One of the main reasons I'm also an SM Contributor.

 

[GC89]

Thats what you get for listening to toyota service techs. The first supra I ever worked on was owned by a guy I worked with. It threw a code 52 occasionally and when he had it at toyota for something unrelated we asked and both techs said a 52 would come up if the engine had predet or if it idled rough enough? we did the rewire anyway in the end

 

[jetjock]

Well, in fairness to professional mechanics they have to know about a lot of cars while I get to focus on only a few.

The ECU has to somehow monitor the health of the knock circuit. In many engines the sensor(s) have an integral resistor connected between the sensor output and case for that purpose but if you ohm a 7M sensor you'll see it's open. So instead of measuring this bit of current to ground the TCCS software listens for normal ignition events.

It does this by opening a sampling window, or gate, on the knock sensor circuit just prior to sending IGt out to the igniter. While the gate is open it expects to hear normal ignition and closes the gate thereafter. The process is repeated for the next cylinder. The same sampling period is used to listen for abnormal combustion. There's more to it but you get the idea.

Anyway, when the circuit goes "deaf" (and certain other conditions are met) the diagnostic system will turn on the MIL and keep it on even if the problem fixes itself. 52 is the only code to do this btw. At the same time ignition will be retarded no more than 10 degrees from calculated. What the knock control system doesn't do is turn on the light when knock occurs.

 

[huntin5L]

Thanks Guys, I already contacted shaeff and will be purchasing the rewire kit.

 

[supraslo]

Erase the codes and try again. if it comes back then begin diagnosing the afm problems. Pull the "ecu" fuse and allow about 20seconds for the ecu to reset, then reinstall the fuse.

 

[RiyadYar]

i got an engine code that my afm is bad. so i went to my box of supra parts and found the balck box that sits ontop the afm. can i just unscrew the one on my car and replace it with the one in my garage?

 

[jetjock]

Sure. Be careful not to lose the O rings. You might want to clean the housing while the electronics are out. *Do not* try and clean the sensor. That said keep in mind it may not be your problem...