Engine error code P0102

[Project1500]

I have a 98 chevy with a 5.7L engine. My service engine soon light came on and I scanned the computer and DTC P0102 came up which stands for Mass Air Flow circuit Low Input. I noticed in my engine fuse block in the section marked ENG 1 that the 20 amp fuse was blown. The truck has a really rough idle, shifts hard and hesitates frequently when cruising down the highway. When I replace the fuse it runs fine. When I hit a speed bump, dip, or any rough terrain it blows immediately and runs like crap.

Its not the MAFS I allready replaced it, and the wires in it are clean. I was thinking it was a short somewhere and whenever I hit a bump it would ground out and blow the fuse. I ran the truck with a good fuse and wiggled all the wires under the hood and couldnt get it to blow. Any ideas of what it might be the problem or any ideas of how to go about figuring out what the problem is?

[Project1500]

Heres the schematic

[Timmah]

Just a quick reply based on your description. Since the fuse doesn't blow all the time and it does when you hit a dip, I am gonna say it is most likely a harness that has rubbed through and intermittently (I hate that word) touching metal somewhere (shorting). I know you probably surmised that much already, but now you just have to find out where, the wiggle test is a good start. take a lok at your schematic(sorry, I didn't) and trace the wiring from the load side of the fuse that is blowing, find the harness on the veh, start the motor and work your way down the harness, wiggling it as you go. You are trying to get the fuse to blow, so push it towards metal if there is some in close proximity to the harness.

I don't work for the manufacturer that you speak of, but here are some most likely places to look for a problem like this.
1. Anywhere you have modified the veh (shock hoop area, cut sheet metal, etc)
2. Added any aftermarket accessories?
3. Near bolted on brackets or tabs or anywhere there is sharp metal (like behind the dash).

Hope that helps,
Tim

[Project1500]

Ok I fixed half the problem. Now I need help with the other half. I replaced the pink wire that goes from my fuse block to my mass airflow sensor with a 16 gauge wire. My fuse doesnt blow anymore whenever I hit rough terrain so there must have been a short somewhere along that pink wire.

The problems I fixed are: no more rough idle at a stop, no more fuse blowing, shifts really smoothly now, shifts into gear really smoothly.

Problems I still have: Slight hesitation whenever I rev the engine, Stumbles, studders when crusing down the freeway every once in a while which it did before when the fuse was blown but not when it was replaced.

Before I replaced the fuse and all the problems would go away. Now that I changed this wire my truck still does half the problems with a new fuse. I dont get it???

[matt_helton]

weeeeell, i think its possible that the MAF sensor could be damaged from all the shorting in the circuit. its really hard to say without scanning it with the TECH2. what your describing could also be totally unrelated to the shorting MAF circuit. its possible that you have an EGR thats opening when it shouldnt and too much when it should be a little, causing a hesitation and stumble. could aslo be an injector problem. check engine light on? the TECH2 would show the cylinder misfire history if there is an injector problem.

did you check all your engine grounds??

and the ground side of the MAF circuit? make sure that its good.

its really hard to say without having the truck in front of me.

[Project1500]

Yes, the SES light was still on and I just got it scanned today. The code that came up is DTC P0340 which is related to the Camshaft position sensor. I looked up the code in my my trucks service manual and noticed on the schematics that the PINK 539 wire goes to this sensor also not jsut the MAFS. Thats the wire that I figured out has the short in it so I ran a new wire to the MAFS. By doing that I bypassed the Camshaft position sensor and also the Oxygen sensor (HO2S bank 1 sensor 1). I could only find three things that the ENG 1 Fuse 21 20 Amp supplies with the PINK 539 wire. The MAFS, CMP Sensor and the O2 sensor. That there completely explains why I still have half the problems because I bypassed those two sensors.

Now my problem is how do I find this short in this PINK 539 wire? What tests can I run besides the wiggle test to determine where the shorts at after I connect the PINK 539 wire back up?

I will post the schematics for the O2 and CMP sensor when I get my digital camera back.

I also need to add that In the begining I thought it was the MAFS so I replaced it which did not fix the problem so I am almost 100% positive its the 539 wire.

[matt_helton]

ok, you said you ran a new wire in the 539 circuit from the ENG 1 fuse to the MAF and the short went away?? right? but by doing this you cut the HO2's and the CMP out of the circuit........am i right?? ok, so make sure you get the the CMP and the 3 HO2's back in the circuit. then if the short is gone you know it was in the wire you replaced. if not then you need to trace the 539 wire to each O2 sensor and up to the distributor(CMP), and yes, the wiggle test is easiest. have a friend help you. according to my diagram i looked up the wires run straight through harnesses to the componnents, should be easy to trace. the only common thing all those pink wires share is splice 108, S108. which should be right near the underhood fuse block. i take that back,.....there one connector that 539 runs through on its way to bank1 sensor2, and bank2 sensor2. its C107. should be under the body up near the frame rail on the pass side, i think. then immediatly after C107 theres one more splice to go to the two sensors i just spoke of........S148

all that probably sounded confusing., sorry, but it really shouldnt be too hard to track down. use a digital multi meter to run continuity through all those sections of the 539 circuit.

[Project1500]

I found the problem and it was a short!!

"ok, you said you ran a new wire in the 539 circuit from the ENG 1 fuse to the MAF and the short went away?? right? but by doing this you cut the HO2's and the CMP out of the circuit........am i right??"

Your right.

"ok, so make sure you get the the CMP and the 3 HO2's back in the circuit. then if the short is gone you know it was in the wire you replaced."

I didnt want to do that because that would look like a horribile wire hack job. Instead I hooked up the the Pink 589 wire again and performed the wiggle test with a new fuse in. I wiggled underneath the drive side floor board by the foot pedals on some wires that came from the 02 sensor and sure enough POP there went the fuse. I saw the 589 wire that was exposed (about half a centimeter was exposed) so I wrapped it up with eletrical tape. I noticed right above the wire was a tiny factory screw that was drilled down through the floor board which overtime rubbed the insulation off the wire. I covered that up with alittle rubber plug and took it for a test drive and no problems!

Before I was mislead because I thought the 589 wire only went too the evap canister purge valve and the MAFS which according to the first scematic above it did. I have had the problem on and off for about a year so Im glad I figured it out because it started to get worse and drove me crazy.

Thanks for the help Matt!

[Project1500]

Matt I was wondering where you got a diagram for the entire 539 circuit? Which manual? I could only find C107,S148, and S108 where it said where they were located. I couldnt find a diagram of where they went.

[matt_helton]

GMSI, its an online General Motors info system. its only accessible through a dealership.

glad you found the problem.