Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Bought it with 100k on it and ran fine for 1000 miles. Then the service light came on with a code of p0101 which points to the MAF. I hooked up the scanner and the MAF has zero signal. I replaced the MAF and no change. It was a rebuilt so i bought another, same thing. I saw the video talking about the ECM possibly being bad. I removed the ECM and cleaned the heck out of it and installed and tested. Cleared the code, was getting a reading from the MAF, ran good for 2 or so weeks. Started it again and the code popped and the MAF has no signal. Removed and cleaned the ECM again to no avail. Would it be wise to just replace the ECM at this point as a troubleshooting step? I cant seem to find a wiring diagram that shows me what pins go from the ECM to the MAF, I was considering just running new lines since the wire bundle is a nightmare in this. Thanks much everyone!!!
I follow your thinking in looking for a wiring/connection issue it certainly would be my first suspect my other suspect would be a cracked soldered joint within the ECU case , but don't rush for a new computer just yet. It would help to know what fault code is being flagged up P0101 ? or P0102 ? or P0103 ?
I would start by checking the power and ground to the sensor, there are different variations of MAF sensors fitted on these vehicles some have more wires than others because on the later type the inlet air temperature sensor (IAT) is built into however 3 of the wires will always be : MAF Signal, Ground and 12v Power.
On GM the MAF Signal wire is usually easy to pick out as GM use Yellow, Black is Ground, Power is usually Orange. Even on a 5 wire sensor the 12v supply is easy to find as it is always next to the Black Ground and Yellow signal.
We are looking to check for near 12vsupply and a good ground
To check the power you should back probe the connector power pin Key On Engine Off and check for 12v supply between the power pin and a good ground.
To check for sensor ground back probe the black wire on the connector and Key On Engine Off first check for between that pin and your good ground this reading should be very very close to zero volts., then unplug the sensor and use a tungsten bulb test light connected to battery +12v to check you have a good ground.
The the wire colour for the MAF signal should be the same at the engine plug so you could try a continuity check on the Yellow between the MAF sensor plug and the ECU plug.
If the sensor passes these simple tests then the next stage would be to check for a frequency signal on the yellow wire with the engine running this needs a multimeter with a frequency scale or an oscilloscope.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Sorry for the delay. Just went out and checked the code and it's a p0102. If I recall I did those checks previously for voltage and ground quite a while ago and they all came back OK. I will check again on Wednesday since I have the day off. Thank you for the thorough response.
I just checked voltages. I have 11.67vdc from positive pin to ground. I have 2.33vdc at the yellow wire. Checked from ground on connector and to battery terminal, both show the same voltage. I'd like to do a continuity to the ecm but I for the life of me, can't find a waiting schematic that shows which of the 4 ecm plug bundles contain the maf sensor wires. It's hard to tell by color cuz of fading and multiple bundles of colors. Also with "To check for sensor ground back probe the black wire on the connector and Key On Engine Off first check for between that pin and your good ground this reading should be very very close to zero volts." Can you elaborate further?
With the help of my son and just going one by one, I was able to run continuity tests to the ecm plug. I unplugged the wire bundles and got continuity from the maf plug to the editor plug.
The signal wire should be 5 volts. Was the sensor disconnected when you measured? This is what I asked for. If it was not, repeat the test. If it was, your ECM needs replaced.
The only thing I could think of other than a bad computer as Paul has already pointed out, is resistance in that wire/circuit.
It seems like nearly every Express van I've ever seen has had near catastrophic corrosion damage to the PCM and it's connectors.
Do you think this is feasible for testing before I order a ecm. Since I know where both wires go into the ecm, could I splice in wires from the plug to near the ecm to eliminate the wiring being a issue? Just for testing of course?
Monde wrote: How about taking the measurement a the ecm itself to see if it makes a difference?
exactly what I would do ^^^^^^
If signal voltage is the same (low voltage) at the ECM pin and at the MAF, you are done! ECM and possibly the connector itself needs to be replaced.
If the maf circuit was dead on the ecm would I get any voltage on that pin? When I view my maf reading on my obd2 I get no response at all. With the signal wire being 2.33vdc would I still not get any response or an incorrect response? I'll check the pin voltage on the next much cooler day, 95 with 76% humidity is intolerable. Have a good 4th everyone
Stegen wrote: If the maf circuit was dead on the ecm would I get any voltage on that pin? When I view my maf reading on my obd2 I get no response at all. With the signal wire being 2.33vdc would I still not get any response or an incorrect response? I'll check the pin voltage on the next much cooler day, 95 with 76% humidity is intolerable. Have a good 4th everyone
IF your signal voltage for the MAF is reading 2.33 volts measured directly at the ECM with the MAF sensor unplugged, your ECM is bad. Any other symptoms or reactions you are seeing are irrelevant. This is a 5 volt pull-down design circuit and is one of the circuits that gets messed up on these boards with water intrusion.
Pulled the ecm plug and the maf sensor plug. Checked vdc at pin 5 of the ecm which is the signal wire for the maf and it reads 2.4vdc. Assuming it's a little higher due to lack of resistance in the line. I'm ordering a new ecm. I'll post once I get the new one installed. Thank you so so much guys.
I got a "new" ecm today installed and the check engine light is off. Good sign. Tried to start it and it starts for a second and stalls. Does this over and over again. Thinking maybe it's a security lock for the key. Anyone have a way to get the security system set for the new ecm?
I looked up security bypass issues and tried the on for 10 minutes, off for 10 seconds 3 times thing and that didn't work. I tried tapping the positive cable to the terminal 3 times and that didn't work. When I start the van it dies right away and the security light flashes. I'm so close to getting her going that this is breaking my heart. Also I forgot to mention and this may be my problem, when I bought the van it had a aftermarket remote start added. I am now thinking that the bypass module isn't coded for the new ecm. I'm going to call a remote installer in the morning and ask for help.
The security relearn can be tricky.
Attempt to start and let it stall, but leave the key in the on position.
The security lamp will be lit for about 10 minutes. Once the lamp goes off, turn the key off for 2 seconds. Then turn the key to the "run" position. (Not crank, if you crank the motor, you need to start again.)
Again, security lamp will light for about 10 minutes. When it goes out, turn the key off for 2 seconds.
Then on again (do not crank the engine). The lamp will be lit for another 10 minutes. When it goes out, turn the key off for 2 seconds. Then on again. After the third cycle, the lamp should illuminate, then go out. When that happens, the van will start again. I've had to to do it as many as 6 cycles and as few as 2.
I like to set a timer on my phone for 9 minutes so i can go do something else and come back in time to not miss the light go out. If you wait too long to cycle the key after the lamp goes out, you need to start again...
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