code 33, car wont start...
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Burning Brakes
Joined: Apr 2005
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From: JUPITER FLORIDA
code 33, car wont start...
I got a code 33, mass air flow sensor. how do I go about trouble shooting the maf? Unit its self, relays...anything else? This is an 86. Thanks guys.
Le Mans Master
Joined: Dec 2004
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From: Myrtle Beach SC
St. Jude Donor '05-'06
First get the Factory Service manual out and follow the troubleshooting flow chart.
If you want to unplug it to see if your car starts that will point to the MAF itself.You can clean it.Gonna have the use the flow charts for the rest.
If you want to unplug it to see if your car starts that will point to the MAF itself.You can clean it.Gonna have the use the flow charts for the rest.
Safety Car
Joined: Dec 2004
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From: Poop land
Yeah, these little bastards can leave you stranded when they go bad! I unplugged mine and was able to go to an auto parts store to get one. I had my foot on both pedals all the time so the car wouldn't stall.
Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Burn the Haynes.
Get the Helm, it has troubleshooting for each code the car can give.
The usual things to check are wiring to the MAF sensor and its relays, then replace the 2 relays (firewall behind battery ~$25), then if all else checks out, replace the MAF sensor.
Get the Helm, it has troubleshooting for each code the car can give.
The usual things to check are wiring to the MAF sensor and its relays, then replace the 2 relays (firewall behind battery ~$25), then if all else checks out, replace the MAF sensor.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
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From: Louisiana
Just finished clearing this code on my 86. I got the FSM and did some troubleshooting. Turns out the MAF burnoff relay was bad as well as the MAF itself. Luckily I had a spare MAF so it only cost me $18 for total fix. 
Thread Starter
Burning Brakes
Joined: Apr 2005
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From: JUPITER FLORIDA
well I checked the relays, disonnected the maf and still no start and now to the burn off, I dont have a picture of the burn off, is it a 3x3 box with like 10 wires going into it? Im poking around in there (near ecm) and so far that is all i see in the mess of wires.
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Le Mans Master
Joined: Oct 2003
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From: seattle WA
Actually the testing for the MAF is quite extensive-maybe Agent 86 will come in and he can post it for you. A few things-either go to ebay or
Helms and get yourself the factory service manuals, I wouldn't burn the Haynes, but for these type of problems you really need to follow the trouble shooting sequence. It could be as simple as 1 of 3 relays, the power relay and the burn-off relay, if you replace1,replace the other. the third-and this is a FSM quote "The oil pressure switch or the ECM, through control of the fuel pump relay , will provide 12 volts for the MAF power relay which provides the 12 volts needed by the MAF sensor." The rest is to lenghty for me to type without the possibility of typos. You can easily throw $100 or more at this problem,
or spend it on the FSM which in turn will save you $100s. Hopefully you'll get some more help-but you'll find there will be other problems.One last thing. Apply 12 volts to terminal G in the ALDL, there should then be 12 volts at the sensor. If no voltage is present, make sure that the fuel pump is running. If not, it's time to check out the fuel pump circuit. See what I mean-and there's other tests like open circuits.Good luck.
Helms and get yourself the factory service manuals, I wouldn't burn the Haynes, but for these type of problems you really need to follow the trouble shooting sequence. It could be as simple as 1 of 3 relays, the power relay and the burn-off relay, if you replace1,replace the other. the third-and this is a FSM quote "The oil pressure switch or the ECM, through control of the fuel pump relay , will provide 12 volts for the MAF power relay which provides the 12 volts needed by the MAF sensor." The rest is to lenghty for me to type without the possibility of typos. You can easily throw $100 or more at this problem,
or spend it on the FSM which in turn will save you $100s. Hopefully you'll get some more help-but you'll find there will be other problems.One last thing. Apply 12 volts to terminal G in the ALDL, there should then be 12 volts at the sensor. If no voltage is present, make sure that the fuel pump is running. If not, it's time to check out the fuel pump circuit. See what I mean-and there's other tests like open circuits.Good luck.
Last edited by rick lambert; Mar 29, 2006 at 10:44 AM.
Drifting
Joined: Mar 2005
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From: GA
Originally Posted by cplonner
well I checked the relays, disonnected the maf and still no start and now to the burn off, I dont have a picture of the burn off, is it a 3x3 box with like 10 wires going into it? Im poking around in there (near ecm) and so far that is all i see in the mess of wires.
This is something I copied from a web page a while back. see if it helps you out at all.
There are three codes that pertain to the MAF sensor: Codes 33, 34, and 36. Code 33 (mass air signal voltage high) is set when the computer sees a high mass air reading at low engine speeds. In other words, there appears to be more airflow through the MAF sensor than the engine can physically breathe at a specific throttle and rpm.
Code 34 (mass air low) sets when the computer registers less than 5 grams of airflow at idle or 2.5 grams/second of air when the engine is first started. The mass air wire inside the MAF sensor should heat up after the car shuts off to clean any contaminants from the wire. When this fails to happen, the computer shows a Code 36 (mass air burn-off malfunction). We'll address and troubleshoot each code individually.
The mass air sensor is a simple design. It's comprised of a wire that heats up when the car is running. The air entering the engine through the MAF sensor cools the wire. The more air ingested by the engine, the more air must flow through the sensor. More air means a cooler wire. The computer knows how much air is entering the engine by the temperature of the wire inside the MAF sensor. The air/fuel mixture is dependent upon having accurate readings from the MAF sensor. If there were a problem, a Code 33 or 34 would be set. Once a Code 33 or 34 appears, the MAF sensor will shut down and the car will go into "basic strategy" mode, aka limp-home mode, until the key is turned off for at least 15 seconds. You'll know the MAF has stopped working when, in Chris' words, "You let off the throttle and it feels like an anchor just dropped."
A Code 33 can be set for several reasons. It appears if the dark green wire (circuit 998) has an open circuit or a bad sensor; if the black, burn-off control circuit wire (circuit 900) has power with the car running; or if the system has a bad ground. You must check for an open circuit on 998 at the ECM on connector B12. There are several places to check for a grounding problem. The cast-iron-headed '85s and '86s have the grounds on the rear of the driver-side head. You'll have to pull the wiper motor to check. The aluminum-headed '86s and '87s have a pack of grounds next to the oil-temp sensor and filter. On the '88 and '89 Corvettes, the ECM, dash, and sensor grounds are on a lower lefthand-side bellhousing stud.
A Code 34 could be set for several reasons as well. A bad ground, an opening in the ducting between the MAF and the throttle body, incorrect minimum idle-air setting of the throttle body, or a worn throttle body can all cause a Code 34. Typically, a worn throttle body or a bad ground will set a Code 34 intermittently (every third or fourth time). To see if the minimum idle air is causing the problem, open the throttle slightly as you try to start the car again. If it's easier to start, check the minimum idle air.
To check the throttle body, simply depress the cruise-control bellows and observe if the throttle-body linkage moves laterally instead of only rotating on the shaft. If there is noticeable movement, your throttle body is worn and the engine is getting unregistered air through the gaps.
'86-'89 Corvettes use a powered fuse link and connector that supplies power to the fuel pump and MAF relays behind the battery. The '85 Corvettes do not use relays for the MAF, but instead use a module next to the ECM. This module rarely goes bad; but to check the module on '85 Corvettes, look for 12 volts at connection E on the MAF with the engine running. Then, run the engine for at least 5 minutes, turn off the key, and check for 12 volts at connection D (MAF burn-off). The powered fuse link is a common cause of intermittent MAF codes. Check the connection and wire for a possible open circuit.
The oil-pressure switch is another possible cause of intermittent MAF codes. If the engine feels as if it has an intermittent hiccup with a fuel pump and MAF code set, the oil-pressure sensor would be the place to start. If the switch is bad, the engine tries to start because power to the pump at startup is fed through the ECM's fuel-pump-relay drive (connection A1).
The relays changed in late '87. Relay No. 14089936 operated the MAF power, burn-off, and fuel pump. Although not always accurate, the connectors for the 9936 relay are the gray connector for the burn-off circuit and the black connector for the MAF power circuit. You'll notice that the new connectors are weather pack connectors to seal out moisture.
To check that the MAF burn-off is getting power, look for 12 volts at the MAF connector position E.
If you get a Code 36, MAF burn-off malfunction, it should immediately reveal itself at startup and it won't affect performance. '85 Corvettes will never show a Code 36, only '86-'89 Corvettes. You can check to see if the ECM is calling for an MAF burn-off by running the car for at least 5 minutes, and checking the black wire at connection F (circuit 900) on the gray connector. It should be grounded for approximately 30 seconds. This is the ECM grounding the wire to actuate the relay. If there is no ground, the ECM is at fault. If you have ground, check the power to the relay. If the relay is sending power to the MAF, check that the dark blue wire (position D) on the MAF sensor connector has power.
(See Previous Caption)
Chris has spent some time adding wires, meters, test lights, and jumpers, chasing down several specific reasons why Codes 34 and 33 will appear. Here is what he found: The dark green wire from the ECM to the MAF (circuit 998) can short to ground or short together with circuit 450 (black or black/white) and cause a Code 34. To get a Code 33, circuits 998 or 450 could have an open circuit. Recently, Chris has seen a few cars for which the only cure was to run new wires for both circuits. This cured the intermittent codes immediately.
Checking The Minimum Idle Air: The first step in checking the minimum idle air is to put the car into Field Service Test Mode. Do this by putting a spade connector into the A and B positions of the ALDL connector. With the key on and the engine off, the fan will turn on and the SES light will flash. Also, the Idle Air Controller (IAC) will fully close.
Code 34 (mass air low) sets when the computer registers less than 5 grams of airflow at idle or 2.5 grams/second of air when the engine is first started. The mass air wire inside the MAF sensor should heat up after the car shuts off to clean any contaminants from the wire. When this fails to happen, the computer shows a Code 36 (mass air burn-off malfunction). We'll address and troubleshoot each code individually.
The mass air sensor is a simple design. It's comprised of a wire that heats up when the car is running. The air entering the engine through the MAF sensor cools the wire. The more air ingested by the engine, the more air must flow through the sensor. More air means a cooler wire. The computer knows how much air is entering the engine by the temperature of the wire inside the MAF sensor. The air/fuel mixture is dependent upon having accurate readings from the MAF sensor. If there were a problem, a Code 33 or 34 would be set. Once a Code 33 or 34 appears, the MAF sensor will shut down and the car will go into "basic strategy" mode, aka limp-home mode, until the key is turned off for at least 15 seconds. You'll know the MAF has stopped working when, in Chris' words, "You let off the throttle and it feels like an anchor just dropped."
A Code 33 can be set for several reasons. It appears if the dark green wire (circuit 998) has an open circuit or a bad sensor; if the black, burn-off control circuit wire (circuit 900) has power with the car running; or if the system has a bad ground. You must check for an open circuit on 998 at the ECM on connector B12. There are several places to check for a grounding problem. The cast-iron-headed '85s and '86s have the grounds on the rear of the driver-side head. You'll have to pull the wiper motor to check. The aluminum-headed '86s and '87s have a pack of grounds next to the oil-temp sensor and filter. On the '88 and '89 Corvettes, the ECM, dash, and sensor grounds are on a lower lefthand-side bellhousing stud.
A Code 34 could be set for several reasons as well. A bad ground, an opening in the ducting between the MAF and the throttle body, incorrect minimum idle-air setting of the throttle body, or a worn throttle body can all cause a Code 34. Typically, a worn throttle body or a bad ground will set a Code 34 intermittently (every third or fourth time). To see if the minimum idle air is causing the problem, open the throttle slightly as you try to start the car again. If it's easier to start, check the minimum idle air.
To check the throttle body, simply depress the cruise-control bellows and observe if the throttle-body linkage moves laterally instead of only rotating on the shaft. If there is noticeable movement, your throttle body is worn and the engine is getting unregistered air through the gaps.
'86-'89 Corvettes use a powered fuse link and connector that supplies power to the fuel pump and MAF relays behind the battery. The '85 Corvettes do not use relays for the MAF, but instead use a module next to the ECM. This module rarely goes bad; but to check the module on '85 Corvettes, look for 12 volts at connection E on the MAF with the engine running. Then, run the engine for at least 5 minutes, turn off the key, and check for 12 volts at connection D (MAF burn-off). The powered fuse link is a common cause of intermittent MAF codes. Check the connection and wire for a possible open circuit.
The oil-pressure switch is another possible cause of intermittent MAF codes. If the engine feels as if it has an intermittent hiccup with a fuel pump and MAF code set, the oil-pressure sensor would be the place to start. If the switch is bad, the engine tries to start because power to the pump at startup is fed through the ECM's fuel-pump-relay drive (connection A1).
The relays changed in late '87. Relay No. 14089936 operated the MAF power, burn-off, and fuel pump. Although not always accurate, the connectors for the 9936 relay are the gray connector for the burn-off circuit and the black connector for the MAF power circuit. You'll notice that the new connectors are weather pack connectors to seal out moisture.
To check that the MAF burn-off is getting power, look for 12 volts at the MAF connector position E.
If you get a Code 36, MAF burn-off malfunction, it should immediately reveal itself at startup and it won't affect performance. '85 Corvettes will never show a Code 36, only '86-'89 Corvettes. You can check to see if the ECM is calling for an MAF burn-off by running the car for at least 5 minutes, and checking the black wire at connection F (circuit 900) on the gray connector. It should be grounded for approximately 30 seconds. This is the ECM grounding the wire to actuate the relay. If there is no ground, the ECM is at fault. If you have ground, check the power to the relay. If the relay is sending power to the MAF, check that the dark blue wire (position D) on the MAF sensor connector has power.
(See Previous Caption)
Chris has spent some time adding wires, meters, test lights, and jumpers, chasing down several specific reasons why Codes 34 and 33 will appear. Here is what he found: The dark green wire from the ECM to the MAF (circuit 998) can short to ground or short together with circuit 450 (black or black/white) and cause a Code 34. To get a Code 33, circuits 998 or 450 could have an open circuit. Recently, Chris has seen a few cars for which the only cure was to run new wires for both circuits. This cured the intermittent codes immediately.
Checking The Minimum Idle Air: The first step in checking the minimum idle air is to put the car into Field Service Test Mode. Do this by putting a spade connector into the A and B positions of the ALDL connector. With the key on and the engine off, the fan will turn on and the SES light will flash. Also, the Idle Air Controller (IAC) will fully close.
Thread Starter
Burning Brakes
Joined: Apr 2005
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From: JUPITER FLORIDA
Ok i dont know if this is weird but this 86 (early cast iron head model) has the little black box near the ecm and the 2 relays behind the battery, didnt your say it would have one or the other morely? The guy at napa said that one of the relays behind the battery is listed as a burn off and the other is the power relay (which is for the fuel pump also). I havent messed with the black box under the dash yet but it is there.
When this thing went bad the problem started as: the car felt like it wasnt getting fuel every few seconds and it would "lag", the check engine light come on, it would run better for a few minutes and then do it again for a few seconds and when i got home and turned of the car then it would not start again.
When this thing went bad the problem started as: the car felt like it wasnt getting fuel every few seconds and it would "lag", the check engine light come on, it would run better for a few minutes and then do it again for a few seconds and when i got home and turned of the car then it would not start again.
Team Owner
Joined: Sep 2001
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Likes: 1,722
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Its going to be one or the other, but you need to replace both.
The black box you are thinking of is not the 85's Burnoff module.
The black box you are thinking of is not the 85's Burnoff module.
Thread Starter
Burning Brakes
Joined: Apr 2005
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From: JUPITER FLORIDA
Originally Posted by vader86
Its going to be one or the other, but you need to replace both.
The black box you are thinking of is not the 85's Burnoff module.
The black box you are thinking of is not the 85's Burnoff module.
So it seems that my other options are wiring
or the pump relay.Is disconnecting the maf and trying to start it an absolute sure way to test it?
Drifting
Joined: Mar 2005
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From: GA
Originally Posted by cplonner
OK, I replaced both relays behind battery, still nothing. What does the black box im talking about do if its not the burn off?
So it seems that my other options are wiring or the pump relay.
Is disconnecting the maf and trying to start it an absolute sure way to test it?
So it seems that my other options are wiring
or the pump relay.Is disconnecting the maf and trying to start it an absolute sure way to test it?
check here for a troubleshooting flow chart. http://chevythunder.com/maf_code_33.htm
Team Owner
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From: Summerland B.C. Canada
Thread Starter
Burning Brakes
Joined: Apr 2005
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From: JUPITER FLORIDA
Originally Posted by Morley
Yes, disconnecting the MAF removes it from the ECM's fueling calculations and puts it in a default fueling mode. If it will start and run with it disconnected 99% ifthe time it is the MAF sensor that has gone bad..the other 1% is wiring or "gremlins".
check here for a troubleshooting flow chart. http://chevythunder.com/maf_code_33.htm
check here for a troubleshooting flow chart. http://chevythunder.com/maf_code_33.htm
Sorry Rick I cant post picks but it is 3x3 roughly, black plastic and has a "computer chip" in it. It is locatated right next to the ecm.It has about 10 wires coming from its connection.
Burning Brakes
Joined: Jun 2002
Posts: 1,001
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From: sd
This is something I did and it saved me some green on a new MAF sensor. Check the pins in the harness that go into the MAF itself. If they are even remotely out of place you could possibly not be making contact with the sensor. I should have done this first when I had a problem with my 85 but I p*ssed around with other stuff for 2 weeks. Everyone else on here has some great info and definitely look for the FSM when you get a chance from www.helminc.com and you'll be good to go for the next problem. Good luck, I know how frustrating it all can be.