blue86iroc

iTrader: (2)

I've been experiencing some surging issues at idle that I have traced to the MAF. I have both the high and low voltage MAF trouble codes, which leads to improper air readings. Not understanding why it (likely) failed, I removed the air intake duct to see if the wire was properly burning off when I turned off the ignition key.

It wasn't.

Now, I replaced the relay about a year ago just out of preventative maintenance, not really knowing if it needed it or not. Instead of buying another one, I checked the relay power wires to see when they were activated... based on the schematic, one would suspect that the black wire from the ECM is grounded when the key is turned off. I jumped between the black wire and one of the orange wires.

Key off, no voltage.
Key on, +12V.

That doesn't make sense; that would engage the burn-off relay when the ignition is switched on.

I also tried a continuity check of the black wire that the ECM grounds when the key is off. It was connected to ground with the key in either position. But, if that's the case, why is there no +12V when the key is OFF since the orange wire is always hot?

As a last resort, I manually jumped the burn-off wires... blue-to-orange. The MAF wire lit right up.

I suspect that the MAF burn-off function hasn't been working for quite some time... and I think that might cause a now-defective MAF sensor. I'm probably going to buy another one, but I want to make sure that the burn-off is working correctly. Am I checking this improperly due to the way the ECM switches the circuit? Is it likely that the relay failed again (or I have the wrong one?)

Trickster

Does your car have the MAF Power Relay in it?

blue86iroc

iTrader: (2)

Yes, the MAF power relay is there. The first time I jumped the burn-off relay, it didn't work because I had the power relay unplugged (diagnostic purposes). Once I plugged it in, the MAF wire burned when hardwired. I haven't checked proper operation of the power circuit yet.

Trickster

I think you might want to replace the MAF power relay.

CashMunson

iTrader: (1)

where is the maf power relay? yesterday I was out driving and my car started running like **** and then the ses light came on. I got home and it gave me a code 33. I pulled the MAF out and it had a tiny speck of dirt on the hotwire which I cleaned off with a qtip. I reinstalled it, unplugged the battery for about 5 minutes to reset everything and still get the same code 33.

blue86iroc

iTrader: (2)

I have three relays on order: fuel pump, MAF burn-off, and MAF power. I think that the relays in the car are working just fine, however.

I first tested the fuel pump relay by turning the ignition to ON and observing the voltage at the relay. It went to 12V for about two seconds and then turned off. As the MAF power relay is tied into the fuel pump relay, it did the same thing -- 12V on the red MAF wire for a few seconds and then nothing. Is this short burst of power only for priming the fuel pump? What supplies power after the car is running?

Then, I started the car. I had full power at both the fuel pump (obviously, if the car's running) and also at the MAF sensor. No problems there.

The burn-off circuitry is still puzzling. With the ignition ON (or the car running), I see 12V across the leads that turn on the relay. However, the relay does not activate... it's almost as if I'm receiving a false reading. I checked the relay to ensure that it was working, too. Furthermore, the black wire that the ECM grounds is not continuous to ground (anymore). There must be a ground loop somewhere, or a short circuit.

Can someone please explain how the MAF burn-off circuitry works? Vader explained it very well here, but I think I need a little more detail.

Trickster

Hello blue86iroc,

I don't know what trouble shooting chart you have been working with but you have been following the wires pretty good. Take a look at this for the burn-off circuit and see if it helps. I also have the one for the MAF sensor.

To CashMunson, your Maf power relay is mounted right next to the MAF burn-off relay and is the same part number.

Trickster

page 2

blue86iroc

iTrader: (2)

Thanks for the diagrams, Trickster. I did some searching and found your other GM service manual pages for Code 33 and 34, which I was also experiencing. I never received a Code 36 per se, but I was pretty sure that burn-off was not occurring. Code 34 disappeared when I reset the ECM, but I decided it wouldn't hurt to go through the diagnostics for each code, anyway.

I followed the prompts for each of the three codes and everything checked out correctly. There were no shorts or unusual behavior. A few of the "conclusions" led to a faulty ECM or MAF sensor. I ordered a new MAF sensor today, so we'll see if that fixes the problem... $160 and a lifetime warranty, so I couldn't complain. The next step will be a replacement ECM.

The Code 36 service page states that burn-off will occur when the engine has "been running for a specified amount of time and the engine warmed up." Do you know the specific numbers so that I can physically check to see if the wire is burning off?

Trickster

I checked all my manuals and found this in my manual for the 85 firebird. The engine must be warm and in the closed loop mode for the MAF burn-off cycle to occur. I would assume that is what is meant by a specified amount of time.

blue86iroc

iTrader: (2)

Thanks . I'll see what I can come up with tomorrow.

blue86iroc

iTrader: (2)

Well, it looks like the problem was the MAF sensor. I put the new one in, reset the computer, and no more MAF error codes. The car is still surging madly at idle, so I have a little more work to do. If it's not the IAC (unlikely, it's brand new), it's probably the ECM or the chip within. The previous owner of my car installed an ADS SuperChip, and I wouldn't be surprised at all if it's been the problem all along. Thanks, Trickster.