'99 Camaro coupe 3.8L auto trans - threw a P0102 which pointed towards MAF sensor. The sensor was recently replaced (used) but it checks out OK according to FAQs and how to in this forum. Also, all o2 sensors were replaced about 10 mo ago. There is also a very good site called troubleshootmyvehicle.com but my meter doesn't measure frequency so used the method here on these forums.

So erased code and drove for a while and threw code again. Started research and discovered that this code can be associated with blown eng sens fuse. Checked fuse and it is blown.

Did more research and read about melted o2 sensors wiring shorting to gnd or to headers or ex manifold blowing the fuse and setting the P0102.

Symptoms -

Drivability seems fine except shifting into drive and rev from a stop is kinda hard and clunky. the rest of the shifts seem a little hard but not too bad. Engine power seems fine, no black smoke, idles fine, etc.. Seem to have lost cruise control though.

P0102 and blown 20A eng sens fuse keep happening ( always together). Can reset code, and put in new fuse and get about 1-2 hrs. drive time then it happens almost always AFTER a stop (engine shutdown) and then about 10 seconds into driving off it happens again.

What I've done -

Researched eng sens circuit - don't know how accurate the schematics I have are, but indicate this circuit feeds MAF, all three o2 sensors and heaters , TCC lockout (brake switch to tell tranny you are on the brakes and to disengage cruise) .

Visual once over - found bare naked wire (insulation completely gone for about 2 inches) that I think goes to knock sensor rubbing against trans case. patched it up and was sure that was the problem but no, blew fuse again. ( since that time have discovered that knock sens is NOT on that eng sens circuit).

More visual - no obvious signs of melted, shorted or bare wires.

Pulled all sensors - inserted fuse - blown when ign turned to "on" ( did this several times). This lead me to believe problem in wiring harness, so this morning, metered the fuse block and got 12V on one side and on other side got continuity to gnd. With all the sensors pulled, there should be NO reading to ground as far as I can tell.

THEN, I got up around harness on pass side o2 and wiggled it around. This time no continuity from "load" side of fuseblock to grnd. (It is reading about .6 kohms or 600 ohms which is not a DEAD short but maybe an oxidized short) Put in new fuse and started reconnecting sensors. got all the way thru with no blown fuse. Drove 1-2 hrs making several stops. Again after one 7-11 pitstop. Light came on about 10 sec after pulling out.

BTW, the hard shifting goes away when the fuse is good.

Unfortunately my multimeter doesn't read freq (Hz) and my Innova CAN OBD2 3110 doesn't give real time data so don't know how far I can go with this but it's eating my lunch.

Question - All these tests have been done cold. Am I OK to disconnect all sensors and drive car to HOT, each time adding a sensor until I get the blown fuse. I realize that codes will be thrown, just don't want to damage PCM or anything.



Any ideas appreciated

 

The best thing would be to get a wiring diagram and follow the circuit associated with the blown fuse. You can drive with the MAF unplugged and it won't cause any damage.

 

Thanks. According to the schems I have, these are on that fuse.:

MAF
all three o2 sensors -
stoplamp switch

Have found the MAF and 3 o2 sensors, where is the stoplamp switch. is it the one on the brake pedal? Reason I ask is b/c on the schematics it shows stoplamp switch and TCC lockout in the same box on the schematic.

MAF - replaced with known good one - still blows fuses.

More clues hopefully to help-

disconnected all sensors ( that I can find) and removed fuse then setup continuity meter on fuse box (load side) to grnd and started plugging o2 sensors back in. beeper went off each time b/c the o2 heater element are all 4.5 ohm so that's ok.

Then disconnected them all again and started wiggling harness. for one second there I got a beep but could not reproduce. This should indicate a short.

clue 2 - put new fuse, reset code P0102 and drove for 20 min. Then shut off car, went to lunch, came back, fired it up and within 10 sec, code and fuse blown. This is now reproduceable.

drive car , shut down, wait 30 min. startup and - fuse blown with code. Now i can't see how a rubbing harness knows to wait unti;l I drive 20 min, shut off, restart and then blow.

Any ideas appreciated.

 

The stop lamp switch is by the brake pedal and is attached to the TCC switch so that the TCC is disengaged when the brake pedal is pushed.

 

Well, down to:

Intermittent short in harness ( but nothing visible near o2 sensors)

seems to be happening after warm so maybe o2 heater is shorting to it's own case when hot ( thanks abe)

although schems don't show stoplamp switch going to grnd, apparently the PCM does provide one when called for so maybe short is thru here.

Have to let this sit for a few days so will keep posted when return,

Thanks

 

is or has there been any amps in the back hatch area? may want to lift that carpet up and see how things look, and yah i would look at the 02 sensors closely. first thing that came to mind when reading first post.

 

No , no audio or electronic mods done to this car.

Need to let the car sit for a few days but...... Too hard to check these o2 sensors hot in-car. Since this happens only when hot, seems logical to me that I could pull them out and CAREFULLY heat up with plumbers torch to see if the heater circuit is either shorting to its own case or the heater coil is dead shorting.

Sound reasonable?

 

thats how i clean em, use a acetylene oxygen set so they heat up clean.