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Code 36 MAF Burnoff Circuit

V

vetter1986

Guest
I have a code 36. Diagnosed the circuit all wiring and relays checkout ok. The diagnostics for the code are very poor. What are the conditions for the code to set, How do you know that the burnoff has taken place. When the code is cleared, vehicle is warmed to closed loop and shut off. Once vehicle is cranked back up the second time, the SES light is on again with a code 36. The code chart makes a point to say not to suspect a faulty MAF. Can anyone help me??????:(
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Relays

If youve replaced them both ( About 20 bucks )
and you still have the problem...remember its measuring a tiny change.. just change em out. Otherwise it's MAF time.
$150.00 @ Kragen ( Just did mine).
How many miles on the engine?

Mike
 
V

vetter1986

Guest
code 36

Relays are good. I have done voltage drops across both burn off and power and both check good.
 

c4c5specialist

Technical Advisor
Joined
May 29, 2001
Messages
3,682
Location
New Haven, Ct. USA
Corvette
Nope, but someday.
Hi there,
This code is for the burnoff function of the MAF.
Basically, this is how it works, once you turn off your engine after a minimum of a 10 min drive. The burnoff function will enable. This will induce 12 volts to the hot wire sensing element, and will make it glow red to 'burnoff' the contamination that may stick to the wire.
Now, according to that, you might want to run the car in your driveway for about 15 mins, and have the front of the MAF off of the airbox. Have someone turn off the car, and you look inside the MAF, You should see the wire in the center of the MAF glow red within a minute or 2. It may last about 15 sec, so watch carefully.
If you dont see anything within the MAF, try this.
Take your multimeter, and monitor the drk blue wire, when your friend shuts off the motor, this should go 12 volts, once the engine is turned off.
Let us know what you have, c4c5:hb
 
V

vetter1986

Guest
code 36

How long should that blue wire go to twelve volts? The manual say for about one second which it does that.
 
V

vetter1986

Guest
code 36

Ok I have voltage on purple for one sec also. Is this enough time for the burnoff?
 

c4c5specialist

Technical Advisor
Joined
May 29, 2001
Messages
3,682
Location
New Haven, Ct. USA
Corvette
Nope, but someday.
HI,
honestly, then I would check your grounding circuit, to make sure that the 900 circuit, which grounds your burnoff relay is constant, as I am suspecting a problem.
if your ground source is longer than your on time of the burnoff relay, therein may be your issue.
1 second usually isnt what I see, it is usually 5 sec, from what I remember.
I have a feeler out for actual on time, but I believe it is 5 seconds.
Please keep me posted, and its good to see another wrench here, c4c5:hb
 

afree029

Member
Joined
Sep 10, 2007
Messages
24
Location
Alabama
Corvette
1988 Silver Coupe
I realize this is a fairly old thread but I am having the exact same problem described and have also done the troubleshooting and discovered that the Burn Off time is only about 1 or 2 seconds. I have read in various places that it could be from 5 to 30 seconds. The switched ground all the way back to the ECM is only 1 or 2 seconds which of course translates to the same burnoff time once you trace it out (12 VDC source applied to burnoff input of MAF after car is switched off) What was the resolution to this thread? what is the burnoff time? Any help would be greatly appreciated.
 

David-F

Well-known member
Joined
Mar 28, 2007
Messages
53
Location
Woodstock,GA
I think you will find the leading cause for this code is the relays, but you can also have a problem with the ECN especialy if you still have thr original 1227165 ECM these were real problems so much so GM replaced them with a new number, but it may have changed again. If I had this code the first thing I would do is replace the two relays checking the connector terminals to be sure they are in good shape if the code returnes you will most likely need an ECM.

David Fulcher
 

afree029

Member
Joined
Sep 10, 2007
Messages
24
Location
Alabama
Corvette
1988 Silver Coupe
MAF Circuitry Operation Summarized - ECM Codes 33, 34 and 36

I have attached an Image of the MAF cicuitry to include the ECM inputs/outputs the MAF Sensor and both the Burn Off relay and the Control Relay.
I did this because it seems that perhaps my request for assistance is not clear.
This may get long winded so bear with me please. I think this info might be useful to others having the same problem. Recurring Code 36.
Basically my question is how long should the burn off period be? 2 seconds, 10 seconds, 30 seconds or whatever it is.
Before I get started let me mention something. The general convention in schematics is to show relays in there static state (no power applied, which is the case with this schematic)
OK here goes. As you can see from the schematic Power is applied to A and D of the MAF Burn Off Relay and C of the MAF Power Relay. When the car is started the MAF Burn Off relay does nothing. This is the normal state of this relay when the engine is running. The coil has not been energized and the switch is open. Also notice that the 12 VDC is also applied to A of the MAF Power relay. As your engine turns during starting the oil pressure builds and closes the oil pressure switch which applies 12 V to D of the MAF Power Relay which energizes the relay causing the switch to toggle to A and 12 V is then applied to E which serves as the power source for the MAF sensor. All pretty simple so far. I have checked all of these functions and they work as they should.
Ok now for the part relating to my question. I am going to make a couple of assumptions here so bear with me.
Assume your engine is warmed and has been running for at least 5 or 10 minutes. You shut the engine off. The oil pressure drops which de-energizes the MAF power Relay then shortly after that occurs the ECM asserts the Ground at F of the MAF Burn Off relay which engergizes the relay, closing the switch which then applies 12 V to E of the Burn Off relay which is also the Burn Off Signal or D of the MAF Sensor. At the same time the 12 V is also applied to C of the MAF Power relay and since it is de-engergized, due to lack of oil pressure (engine off), the 12 V is routed from C to E of the MAF Power Relay and to E of the MAF Sensor itself to supply power to the sensor. Now here is the part that most folks seem to have a problem with. I think everyone assumes that since the engine is off the MAF and the ECM are no longer active. This can't be the case. I have to assume since there is no signal to the ECM from the MAF Burn Off relay itself that the ECM has enough smarts to read/sample the MAF Signal, C of the MAF Sensor during the Burn Off period. After all don't forget the ECM is the guy that asserted the signal to begin with. I have to also assume that the ECM has enough smarts to know that when 12 V is applied to the Burn Off Signal D that is should produce a certain output on the MAF Signal to the ECM. This is the only way the ECM can know which code to set. In my case it is setting a 36. So this brings me to my question or questions I should say. The Service Manual covers Codes 33 and 34 very well and tells you exactly why the fault was set but it is vague at best about a code of 36. Basically a code 33 indicates the ECM has seen a HIGH air flow input , greater than 2.2 Volts of MAF Signal, just after the engine was started and 34 indicates the ECM has detected a LOW air flow signal, low voltage at MAF Signal input to the ECM just after the engine. Now since my ECM is not setting either a 33 or 34 and the same input is used to decide whether or not to set the 36 I have to assume the ECM is ok.
Ok finally the questions.
One, how LONG should the burn off signal be asserted? On my 88 it is only about 1 or 2 seconds and I don't know if this is long enough for the MAF sensor to turn on, stablilize, produce the correct output based on the 12 V Burn off signal input or not. And Two, when the burn off signal is applied what value is to be expected at the MAF Signal input to the ECM as read with a typical DVM. I also have an oscilloscope if anyone can tell me what to expect I can look at it with the scope as well. ( I suspect my problem is the signal is not asserted long enough, or there is something simply wrong with the MAF. Perhaps an open in the Burn OFF input signal path internal to the MAF. Maybe this is the reason the assertion period of the signal is so short. Maybe the ECM sees that the MAF did not respond the Burn Off input signal and simply decided to set the 36 code and remove the ground. Maybe not in that order. A lot of maybes?
I apologize for the long winded nature of this post but I wanted to be sure that those reading understand why I am asking my questions.
 

afree029

Member
Joined
Sep 10, 2007
Messages
24
Location
Alabama
Corvette
1988 Silver Coupe
I decided to run another test. I simply applied 12 V to E of the the MAF Sensor Burn Off relay with the relay removed. See attachment in previous post. While doing this I watched the inside of the MAF sensor. As soon as the voltage was applied the sensor wire turned a bright orange (which means it got really hot which is exactly what it is supposed to do.) So I have at least eliminated the Burn Off Circuit in the MAF itself. I am now leaning toward the MAF signal output but that seems unlikely since it does not set codes 33 or 34. The next test I run will be to supply power to the MAF sensor while monitoring the MAF signal output. I will then activate the burn off circuit for a second or two and note the voltage reading out of the sensor. This could be useful info.
 

afree029

Member
Joined
Sep 10, 2007
Messages
24
Location
Alabama
Corvette
1988 Silver Coupe
OK I ran the test I described in the previous post. Monitor the MAF output while activating Burn Off Circuit and MAF power control circuit. I don't know what the safe time frame is keeping the Burn Off activated so I tried to simulate the time frame I have measured which was about 1 or 2 seconds. The voltage level range from around 1.7 up to 2.5. I did this several times with varying results but again I only activated the circuit for a short time. Still need to know what should it be. At this point I guess I have to surmise (1) either the MAF sensor itself is not resonding as the ECM thinks it should during the Burn OFf Cycle or (2) the ECM, for some reason, is not asserting the ground to activate the circuit long enough to get a good reading.
I should add I have the following publications as reference 1988 Corvette Service Manual Set, GM Code Scanner with Manual, Haynes Manual, and the Chilton Fuel Injection and Electronic Engine Controls 1984 - 1988 Domestic Cars and Trucks. I have scanned all of these and not one of the mention the time period for the burn off. Some of them describe the series of events that occur but leave out that one little detail (how long).
 

afree029

Member
Joined
Sep 10, 2007
Messages
24
Location
Alabama
Corvette
1988 Silver Coupe
The next test I am going to do is simply disconnect the MAF input to the ECM and see if I can force a 33 or 34 error code. This is more of a sanity check than anything.
 

afree029

Member
Joined
Sep 10, 2007
Messages
24
Location
Alabama
Corvette
1988 Silver Coupe
OK I removed the MAF and started her up. Scanned the codes and sure enough I now have a 33 in addition to the 36 I had before. The 33 code makes since since the MAF input is actually pulled up to 5 volts through a current limiting resistor. Which means with the MAF disconnected the ECM should have been seeing the full 5 VDC. The ECM responded as it should have by detecting the level was higher than the 2.2 VDC as the service manual states and set the code. The MAF signal actually drives the voltage down depending on various conditions. This tells me the wiring is OK from the sensor to the ECM. Hmmmm what next??? I have read that a code 36 does not affect performance but I'm not sure if I buy that. If the sensor does not respond correctly to the burn off cycle then why should we expect it to perform correctly under normal operating conditions. I mean the voltages may be within a tolerance window that does not set the 33 or 34 codes but it may also mean you are not getting optimum performance from your engine if the sensor does not respond quickly and predictably. Food for thought.
 

JKCaston

New member
Joined
Oct 6, 2007
Messages
1
Location
SW Michigan
Corvette
1983 Jaguar 350 TPI Conversion
afree, excellent set of posts. I wanted to add the following:
I am seeing virtually identical symptoms to you on my 86 305 TPI, code 36 everything else seems good. New burnoff and power relays, same results. My voltages are as follows:
-During burnoff: MAF signal = 2.4 VDC, wire turns red, but cycle is only a second or two
-During engine idle: MAF signal - approx 1VDC, voltage increases with RPM's
-I have isolated the neutral switch, it is definitely grounded.
-My oil pressure switch does not appear to be intermittent, but I am going to ground it next.
-Most importantly, I dropped 90 bucks on an Ebay ECM. Works great, EXCEPT I still have the Code 36 after 1 engine warm up/shut down cycle.

Very frustrating, do you you have this one figured out yet?! Any thoughts on some posts that refer to crankcase pressure causing this?
 

afree029

Member
Joined
Sep 10, 2007
Messages
24
Location
Alabama
Corvette
1988 Silver Coupe
afree, excellent set of posts. I wanted to add the following:
I am seeing virtually identical symptoms to you on my 86 305 TPI, code 36 everything else seems good. New burnoff and power relays, same results. My voltages are as follows:
-During burnoff: MAF signal = 2.4 VDC, wire turns red, but cycle is only a second or two
-During engine idle: MAF signal - approx 1VDC, voltage increases with RPM's
-I have isolated the neutral switch, it is definitely grounded.
-My oil pressure switch does not appear to be intermittent, but I am going to ground it next.
-Most importantly, I dropped 90 bucks on an Ebay ECM. Works great, EXCEPT I still have the Code 36 after 1 engine warm up/shut down cycle.

Very frustrating, do you you have this one figured out yet?! Any thoughts on some posts that refer to crankcase pressure causing this?
This one had me going for a while. Turned out to be an intermittent connection on the MAF sensor plug, harness side. What made it so difficult is that the connection seemed to be good most of the time when I had the MAF set in a position where I could watch the burn off wire when I engergized the relay. I guess the added stress on the connector due to the fact that I had it turned sideways seemed to make a good connection. However when I installed the MAF as it normally should be I would get the fault. I finally ended up installing the MAF as it normally should be but disconnecting the air filter side. I then set a small mirror up so I could watch the burn off wire. It was then that I discovered that when the MAF was mounted correctly the connection rarely was good and the Burn off did not occur. Hope this helps.
 

fatboyreyn

Well-known member
Joined
Aug 31, 2006
Messages
116
Location
east coast
Corvette
1986 red
I experienced a code 36 a while back. I replaced both relays and MAF sensor, after many hours od troubleshooting, per service manual. I made the mistake of going with aftermarket products. After paying a pretty penny for an OEM Bosch MAF sensor, I still had the code, although the car ran 10 times better than the aftermarket MAF. I then replaced the burnoff relay with another new one, only this time an OEM Delco relay and code went away and has been good for 1000 miles now. Just thought I'd add my 2 cents.
 

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