Hey guys, I've been a member for a while but this is my first post as I've found all previous questions by searching. Well here it is, my 88 IROC 305tpi is throwing code 34 as the title says. I checked green wire at c on the maf plug and there was no voltage. I probed the maf plug while the car was running and there was 12 volts from the red a wire with the negative dvm lead on the black/white e wire, also there was 5 volts at terminal c when I grounded the negative lead to the b black wire so it seems to me that the plug to the maf has the correct voltage. Now when I plug in the maf sensor there is no voltage at the c wire whether I ground it to a bolt or the black b wire which is the ecm ground. I swapped in a maf that was working on another vehicle and still no voltage, and then I swapped in a good ecm and still no voltage. All relays work as they should including the fuel pump relay which powers the maf relay. I am at a loss here because everything seems to be as it should. The ecm is giving the 5 volt signal to the maf until I plug in the sensor and the power to the maf(12 volts) is ther as well. Am I missing anything here? Any help will be greatly appreciated.

 

I just wanted to add that my chilton's manual only lists diagnostic steps for speed density computer with code34. Can someone post a link for maf code 34? Thanks.

 

IIRC the fuel pump relay does not energize the MAF relay. Switch the MAF relay and the MAF burnoff relay..IE plug the MAF relay harness into the MAF burnoff relay and vice versa. If my guess is right it should now trigger a code 33. I think you have a bad relay.

 

Thanks for your response. I used the fan relays, which are both fairly new and I know they work, to switch the 2 maf relays and the problem was still there although you are right that I also have code 33 now and 36. I thought the tan/white wire from the fuel pump relay brought power to the maf relay but I could be wrong. Either way the maf sensor is getting 12volts at the red (E) power wire. I also verified the grounds on the maf plug using the 5volt wire from the TPS as I saw in another post and they were both good. One thing that I read that I have not checked yet is for leaking injectors. Does anyone if that would cause the voltage at the maf to ecm(C) wire to be so low as to read .01 VDC because that is what I keep getting. Thanks.

 

You just isolated your own problem if you switched the MAF relay and the MAF burnoff relay and you now have a code 33/36 instead of a code 34. Go buy a new MAF relay and a MAF burnoff relay and enjoy the rest of the day. If the codes changed by simply swapping the relays then the relays are the problem.

 

I switched the maf and burn-off relays with two that I knew were good and I got code 33 and 36 in addition to 34. I'm going to disconnect the battery to reset the ecm and try that again and hope that works. Thanks again for your input.

 

The MAF power relay is not exactly the same as the burn off relay or a fan relay. the MAF power relay MUST have a normally closed contact to permit power to the sensor during the burn-off cycle:

 

I did not realize they were different, I hope I didn't mess anything up by switching them. Thank you so much for the diagram, for some reason Chiltons only has the diagram for the MAP cars. I'll get the new relay and post the results.

 

Well, I replaced both relays and I'm back where I started with a code 34. When I test the output wire from the maf to the ecm I get .01 or .02 VDC, which is basically no voltage because just touching the voltmeter leads will read that. When opening the throttle it does not change at all and when I start the car the SES lights up within 5 seconds and stays on until I shut the car off. The only other symptoms are: sometimes it takes a few trys(cranking for 3 or 4 seconds) to get it started, when driving the car everything is fine until I come to a stop or slow down to turn then it immediately stalls no chugging or anything it shuts off cleanly, also if I put it in nuetural and let off the gas the revs drop and it stalls but the wierd thing is if I tap the accelerator as its about to stall it revs up and drops to a normal idle without stalling. The only other symptom is fouled plugs. I'm starting to think that something else is wrong causing the MAF to read low voltage. Can anyone think of other things that may affect this? I did check the TPS and it is .54 at idle and smoothly rises to 4.96 when opening the throttle. What else can cause this?!!! Please help!!!

 

Car running?
No power at the red wire? Test it right out of the relay. No power? Test the wires going into the relay. Pwer? Bad relay. I don't think you'll get a signal out of the maf if the car isn't running. I don't recall the scale from idle to WOT of the readings. Vader'll have that at the tip of his fingers.

Oh, yea. Paragraphs.

 

The car starts up and seems to run well, but the SES light comes on after about 5 seconds and stays on the whole time it is running.

Here is where I'm at:

-With the car running there is 12 volts at the red wire on the relay

-There is 12 volts on the red wire at the MAF plug (car is running)

-All grounds have been verified many times over

_Unplug the MAF while the car is running, ground DVM, red DVM lead to MAF plug red wire reads 12.72 volts

-Negative DVM lead to MAF plug black/white ground wire, positive DVM lead to MAF plug red wire reads 12.72 volts (car still running)

-Ground DVM, positive DVM lead to MAF plug green 'c' wire reads 4.96 volts (car running with MAF unplugged)

-Negative DVM lead to black 'b' ecm ground wire, positive DVM lead to green 'c' wire at MAF plug 4.96 volts (car running MAF unplugged)

-MAF and burnoff relays are new and have been verified to be working correctly

-ECM and MAF have been replaced with ECM and MAF from car that ran perfectly

THE PROBLEM: With MAF pluged in and car running green 'c' wire reads .01 or .02 volts at all times from idle to WOT and all points in between whether I ground DVM to engine bolt or to black 'b' wire it never changes. ALDL shows code 34.

Did I miss something?

What else could cause this to read that low voltage at all times?

I have triple checked the TPS and it reads .54 at idle and smoothly rises to 4.96 when openeng the throttle.

Any help or suggestions at this point will be greatly appreciated!!!!

 

I am sure you have looked at this a hundred times already but does the terminal lead actually contact the pin on the maf for the signal input???

I will look at the shop tomorrow to see if I can find anything in the MAF diagnostics that would cause no input signal. Did you try the different MAF sensor before or after the relays were swapped out???

 

Razor, it's funny you should mention the maf plug terminals because I ordered a new plug from TPI pats.net. At this point it is the only thing I can think of to try and change. I've swapped the other MAF back and forth before and after replacing relays. Please let me know if you come up with anything else that could cause this.

If something else was wrong that is making the voltage read almost nothing (.01 or .02volts) wouldn't it at least rise a little when opening the throttle?

When the ECM goes into limp-home mode does it comepletely ignore the MAF output?

This is starting to drive me crazy, I just dont want to take it to a shop and have them throw parts at it at my expense or charge me labor to repeat all the troubleshooting I've already done. There has to be an explanation for this. Thank you to all who have responded to this thread. Anymore thoughts or suggestions will be greatly appreciated.

 

With the ECM in open loop, the ECM will essentially ignore the MAF input for fuel calculations. It still monitors the signal, however.

Make sure the MAF has full battery voltage on the "E" terminal whenever the ignition is on. Make sure there is NO voltage on the "D" terminal with the ignition on. And make sure that BOTH the "A" and "B" terminals are solidly grounded. Any resistance to ground on the "B" terminal will render the MAF signal useless.

You should expect to read somewhere in the range of 700-900mV from the "C" terminal with the engine idling and MAF connected.

Dumb question, but are you certain the MAF is installed with the flow in the correct direction? There is a big arrow molded in the housing indicating proper air flow direction.

 

I'll check the installation but I remember seeing the arrow so it's probably right. While I'm at it I'll recheck everything again. Thanks for the input, please keep it coming.

 

I may be confused here...

When you read the 'c' terminal on the MAF itself? or the wire? with the car running and MAF unplugged you read 4.9v

When you apparently backprobe the 'c' wire with it plugged in and the car running you only get .01v to .02v?

That doesn't make sense to me. Do verify that it isn't mounted backwards. I would concentrate over the 'c' terminal/wire reading.

Also, you may want to try and adjust the TPS to read a little lower as it has a relationel effect to the MAF reading to throw the code.

 

Red Devil, you read that right, with the car running and the MAF unplugged I get the 4.96VDC reading on the 'c' terminal of the MAF plug, then, when I plug in the MAF I get the .01 or .02VDC when backprobing the plug at the 'c' terminal.

It makes no sense to me either, and I double checked the installation of the MAF sensor and it is correct.

I just recieved the new MAF plug and installed it and I get the same readings. I will try adjusting the TPS and see if that helps.

I'm beginning to wonder if something fried the replacement MAF. It came from a car that ran perfectly, however I have no way of rechecking that as most of the car is parted out already. What are the odds of having 2 MAF sensors with the exact same problem?

What else can cause a code 34?

 

Is this true of just the 86-87 MAF systems or all the way thru to 89?

Reason , I ask is because I replaced both for an 89 from over the counter GM parts and the relays were the same part#'s.

Or is it that the replacements are dual use relays?

Or did I just make the mistake of disabling the burn off.

 

I have a 86 Iroc TPI and im gettin the same code...code 34. I just tried swapping my relays and disconnected the battery and its still the same...code 34. any ideas on that one? the car seems to run good, but pops the code right away.

 

I had the same problem and two different Chevrolet dealerships told me that the relays were different. I found four relays on my car which were all original parts and all had the same part numbers. The dealer only replace one and told me that the others were fine yet I still kept getting the codes. After much frustration and after replacing my MAF and my ECM I just decided to replace all of the relays myself. I used exactly the same parts (all carry the same number) and the problem cleared up instantly. Your case my be completely different but there seems to be a lot of confusion about the relays so if I were you I would just replace all of them like I did. Hope that helps.

 

I got two relays (same part #) for the MAF Power and Burnoff. They would only fit the one (think it was the power relay). The other one was too tight to fit.