Engine Dies While Driving - MAF Code, Not the MAF
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I take it you are using the harness with the low beam light bulb with one lead attached to the battery positive terminal while moving the other lead around to various ground points to check current flow through those grounds.
PCM and MAF Sensor grounds are spliced together at Splice 120 and the splice is grounded at G106 which is on the engine above the starter. The PCM establishes reference voltages for various sensors. If it's ground connection is dirty/corroded the reference voltages can be off by some voltage level. The electronic signals used for various sensors operate on voltage levels in the +5V range and resistance raising corrosion that might not affect a light bulb may be enough to cause a shift in reference voltage levels.
Also check to make sure you have +12 V at the Under hood Electrical Center and if you can at the PCM.
Bill
PCM and MAF Sensor grounds are spliced together at Splice 120 and the splice is grounded at G106 which is on the engine above the starter. The PCM establishes reference voltages for various sensors. If it's ground connection is dirty/corroded the reference voltages can be off by some voltage level. The electronic signals used for various sensors operate on voltage levels in the +5V range and resistance raising corrosion that might not affect a light bulb may be enough to cause a shift in reference voltage levels.
Also check to make sure you have +12 V at the Under hood Electrical Center and if you can at the PCM.
Bill
With cold, snow, and/or muddy roads, I've not done much with this. You're correct, Bill, on the methodology for checking current flow. Nothing seems out of the ordinary, and I have no reason to believe there are any ground-related issues going on.
With the weather looking pretty nice, it's looking like time to put a little more effort in and see what I can figure out. Stumped on where to go. I'm thinking I can back-probe the MAF sensor and see if it's possibly seeing a surge or dip when the issue occurs. Not sure my Fluke is fast enough to register that, but we'll see.
What makes no sense is that whatever is happening is enough to kill the engine, and clearing that code is sufficient to restart it.
Any ideas guys?
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Last edited by C5 Diag; Mar 16, 2020 at 07:16 PM.
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From: Anthony TX
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St. Jude Donor '08
If you are having MAF, IAT issues, you could be having a wiring problem.. Look at the engine wiring harness at the rear of the engine around cylinder #7 fuel injector. That main harnesses ( that contains all of the MAF, IAT wires) bends around a black metal bracket at the rear of the engine. That bracket can and sometime does chafe the harness and wires inside that harness,
Seen it happen on several C5s. If the wrap on the harness is cut or rubbed through, there's a good chance the wires are also.
Recommend you use the DIC Code reader and CLEAR all of those old history DTCs. That way you will know if any DTCs reappear, they could be relevant.
Seen it happen on several C5s. If the wrap on the harness is cut or rubbed through, there's a good chance the wires are also.
Recommend you use the DIC Code reader and CLEAR all of those old history DTCs. That way you will know if any DTCs reappear, they could be relevant.
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Just because you replaced the ignition switch some time ago does no mean that the "new" one has not gone bad. My car's original ignition switch lasted 12 years, the second, also an AC Delco lasted 2 years. Now the third one, another AC Delco has been in service for 6 more years. OK so far.
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Just because you replaced the ignition switch some time ago does no mean that the "new" one has not gone bad. My car's original ignition switch lasted 12 years, the second, also an AC Delco lasted 2 years. Now the third one, another AC Delco has been in service for 6 more years. OK so far.
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If you are having MAF, IAT issues, you could be having a wiring problem.. Look at the engine wiring harness at the rear of the engine around cylinder #7 fuel injector. That main harnesses ( that contains all of the MAF, IAT wires) bends around a black metal bracket at the rear of the engine. That bracket can and sometime does chafe the harness and wires inside that harness,
Seen it happen on several C5s. If the wrap on the harness is cut or rubbed through, there's a good chance the wires are also.
Recommend you use the DIC Code reader and CLEAR all of those old history DTCs. That way you will know if any DTCs reappear, they could be relevant.
Seen it happen on several C5s. If the wrap on the harness is cut or rubbed through, there's a good chance the wires are also.
Recommend you use the DIC Code reader and CLEAR all of those old history DTCs. That way you will know if any DTCs reappear, they could be relevant.
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From: Anthony TX
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The actual connectors that plug into the Ignition Switch can also have issues.
The female pins in the harness connector get spread apart and can make poor connections Especially the large power pins. The connection between the male and female pins can get so bad that it melts the connector body cell where that pin rest.
Check the two connectors for spread female pins!
Bill
The female pins in the harness connector get spread apart and can make poor connections Especially the large power pins. The connection between the male and female pins can get so bad that it melts the connector body cell where that pin rest.
Check the two connectors for spread female pins!
Bill
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Do you see any fluctuations on the 5v reference signal? I'm seeing it fluctuate about 1 V on the same frequency as the signal. Using the middle ground terminal on the MAF for a ground reference.
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North of Hartland, South of Fenton.
Going to check out both the '98 and my '01 to see if there is anything telling and anything different between the two. Did a quick look at the '98 to play with the scope a little.
Do you see any fluctuations on the 5v reference signal? I'm seeing it fluctuate about 1 V on the same frequency as the signal. Using the middle ground terminal on the MAF for a ground reference.
Going to check out both the '98 and my '01 to see if there is anything telling and anything different between the two. Did a quick look at the '98 to play with the scope a little.
Do you see any fluctuations on the 5v reference signal? I'm seeing it fluctuate about 1 V on the same frequency as the signal. Using the middle ground terminal on the MAF for a ground reference.
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How exactly are you testing the 5 volt ref ??...connector unplugged probing the yellow wire ??...if so that 5 volts should not fluctuate !!...with the connector plugged in using a voltmeter you will only see about 2.5 volts or so...the average of that squarewave in my pic...voltmeter testing is not the right way to test a MAF sensor...a voltmeter just doesn't update fast enough...scope is best followed by checking frequency, and then voltmeter
The MAF doesn't use a 5v reference. It uses straight ignition voltage.
I must have had something with a bad back-probe previously.
Checked out my '01 and rechecked the "98 for comparison. Just running at idle for both. The ign voltage is ~14v as expected. The frequency signal fluctuates from 5v to 0 as expected, although the frequency and bandwidth of the signals is slightly different between the cars.
Strange though, and possibly a clue (not knowing what changed from 98 to 01 in the ecm) is that the 01 continues to run when the MAF is unplugged. The '98 dies.
And I'm using a Digilent Analog Discovery 2
https://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/
Last edited by ddecart; Apr 1, 2020 at 09:18 PM.
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Actually, scratch all that 5v reference nonsense.
The MAF doesn't use a 5v reference. It uses straight ignition voltage.
I must have had something with a bad back-probe previously.
Checked out my '01 and rechecked the "98 for comparison. Just running at idle for both. The ign voltage is ~14v as expected. The frequency signal fluctuates from 5v to 0 as expected, although the frequency and bandwidth of the signals is slightly different between the cars.
Strange though, and possibly a clue (not knowing what changed from 98 to 01 in the ecm) is that the 01 continues to run when the MAF is unplugged. The '98 dies.
And I'm using a Digilent Analog Discovery 2
https://store.digilentinc.com/analog...-power-supply/
The MAF doesn't use a 5v reference. It uses straight ignition voltage.
I must have had something with a bad back-probe previously.
Checked out my '01 and rechecked the "98 for comparison. Just running at idle for both. The ign voltage is ~14v as expected. The frequency signal fluctuates from 5v to 0 as expected, although the frequency and bandwidth of the signals is slightly different between the cars.
Strange though, and possibly a clue (not knowing what changed from 98 to 01 in the ecm) is that the 01 continues to run when the MAF is unplugged. The '98 dies.
And I'm using a Digilent Analog Discovery 2
https://store.digilentinc.com/analog...-power-supply/
"Actually, scratch all that 5v reference nonsense.
The MAF doesn't use a 5v reference. It uses straight ignition voltage"
Sorry to inform you but the MAF does indeed use a 5 volt ref. If you didn't know there are MANY circuits that use a 5 volt ref.in the C5 and it's the most important electrical circuit in the car. The "straight" ignition voltage is ONLY used to keep the hotwire inside the MAF at a temp 200 degrees centigrade above ambient !!...here's some videos should you doubt me...good luck in your troubleshooting !!
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"Actually, scratch all that 5v reference nonsense.
The MAF doesn't use a 5v reference. It uses straight ignition voltage"
Sorry to inform you but the MAF does indeed use a 5 volt ref. If you didn't know there are MANY circuits that use a 5 volt ref.in the C5 and it's the most important electrical circuit in the car. The "straight" ignition voltage is ONLY used to keep the hotwire inside the MAF at a temp 200 degrees centigrade above ambient !!...here's some videos should you doubt me...good luck in your troubleshooting !!
The MAF doesn't use a 5v reference. It uses straight ignition voltage"
Sorry to inform you but the MAF does indeed use a 5 volt ref. If you didn't know there are MANY circuits that use a 5 volt ref.in the C5 and it's the most important electrical circuit in the car. The "straight" ignition voltage is ONLY used to keep the hotwire inside the MAF at a temp 200 degrees centigrade above ambient !!...here's some videos should you doubt me...good luck in your troubleshooting !!
The 3-wire MAF has:
Yellow: Mass Air Flow (MAF) Sensor - Signal
Blk/Wht: Ground
Pink: Ignition
The MAF likely creates its own 5V ref internally, but there isn't a 5V feed into it.
I think I had a bad connection on the back-probe on the pink wire to the point I was getting a variable voltage reading that wasn't actually there.
Last edited by ddecart; Apr 2, 2020 at 08:56 AM.
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I've been around testing for over 20 years. I'm very familiar with 5V reference signals. The MAF doesn't have one as an input.
The 3-wire MAF has:
Yellow: Mass Air Flow (MAF) Sensor - Signal
Blk/Wht: Ground
Pink: Ignition
The MAF likely creates its own 5V ref internally, but there isn't a 5V feed into it.
I think I had a bad connection on the back-probe on the pink wire to the point I was getting a variable voltage reading that wasn't actually there.
The 3-wire MAF has:
Yellow: Mass Air Flow (MAF) Sensor - Signal
Blk/Wht: Ground
Pink: Ignition
The MAF likely creates its own 5V ref internally, but there isn't a 5V feed into it.
I think I had a bad connection on the back-probe on the pink wire to the point I was getting a variable voltage reading that wasn't actually there.
Last edited by C5 Diag; Apr 2, 2020 at 09:31 AM.
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I need to upload some screen shots as well. That'll probably help.
Still puzzled at the difference between the two with the MAF disconnected. 01 runs, 98 dies. Suggests that speed density on the '98 isn't happy.
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Here is the scope data from yesterday with both cars while idling. '98 on top, '01 on bottom. I didn't look at the idle speed for either of them to justify the frequency difference.
