3 DTC's & I keep blowing the ENG SEN 20 amp fuse...PLEASE HELP!

[DOC-Z]

I have a basically stock 2000 Firebird V6 (3.8 litre or 3800) with a manual transmission and about 92,000 miles. For months I have been trying to fix a check engine light. The code will go away if I clear the codes and swap the 20 amp fuse for the ENG SEN. (Engine Sensor) under the hood. Once this is done, the check engine light will remain off anywhere between 5 minutes to 3 days. The engine codes which are coming up are:

P-0131 O2 Sensor Bank 1 sensor 1
P-0133 O2 Sensor Bank 2 sensor 1
P-0101 Mass Air Flow (low voltage)

The main symptom that I've been having with the car is when I shift the car into neutral and coast to a stop, the idle will bounce (or jump). It will start jumping a little bit and go between 700 to 1200 RPM. The longer I coast and let the car idle in neutral while moving it will eventually continue to worsen and bounce between 500 to 2000 RPM. The lights will subsequently flicker, fan will slow (if on) and the entire electrical system will bounce like this until I slow to around 15 mph or stop. Then, it will all go back to normal as the RPM's level to a normal idle. In other words, it continually ramps up the bounce the longer it is let to do so. If I'm at a stop, the idle is normal. If the car is parked at idle, in gear and running, etc., there are no problems. It accelerates fine, the fan, lights, radio and everything is normal. If I swap out the 20 amp fuse and clear the codes, the problems (again) stop...as long as the check engine light is off, everything is fine. Once the check engine light comes back on and I'm driving the car (coasting) the problem begins again / re-occurs.

So you know which fuse I'm talking about, here is a picture of the fuse cover under the hood and the fuse. Because I've replaced it so many times, it's the odd looking yellow one:

Also, ON OCCASION, the car will start but shut off right away and NOT stay running. If you turn the key off, wait for a few seconds, and restart it, the car will start like normal and remain running. This has only happened 3 times since the check engine light came on a few months ago. I'm sure there is some sort of connection between the 2 things going on, but not 100% positive.

I've cleaned every ground wire I could find and replaced one which was crispified. I removed the fuse panels under the hood and cleaned the ground and terminals as well. The problem still persists and I don't know where else to look. I spoke to GTWolf who had a friend who had a similar problem, but he didn't remember where the short was and what he did to correct it. Does anyone have a clue as to where to look to find this short, because I'm out of idea's? Like I said, I've been futzing around with this for months.




**** I've done some research and found that the filamment on the MAF sensor is self cleaning. When the car is shut off, a burst of electricity runs through the filament. The purpose of this is to bring the filament temperature up to 1000 degrees for .01 seconds to burn off contaminents. After I clear the engine codes and change the fuse, the check engine light comes on while I'm driving...not when I initially start the car. ***

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[Eagle]

Have you inspected the o2 sensor harnesses completely?

sounds like a crappy problem to solve!

 

[JDHedman]

Just replace it with a 40 amp fuse you'll be good

let me see if I can find anything helpful in alldata for ya

 

[DOC-Z]

EAGLE: Yeah...that's the funny thing. When it started, there was only 1 code, O2 Sensor 1 Bank 2. The it happened again, but Bank 1 Sensor 1. I wound up replacing both Oxygen sensors. Then the problem started again, but I was getting all 3 codes. To date, I have not gotten any additional codes.

I took the car to Vato Zone, Advance and Nye Auto Doctor in McHenry and they all said the MAF is and looks fine. To be sure/sure, I tried using MAF Sensor cleaner...which did nothing. Being it was all 3 codes, that there was probably a short somewhere and I opted NOT to replace the $200 sensor...being I already replaced both O2 sensors and the problem hasn't changed.


JDHedman: I would appreciate any sort of suggestion. I was thinking a 25 amp fuse, but I don't want to burn out the sensors.

 

[JDHedman]

to start

 

[JDHedman]

CIRCUIT DESCRIPTION
The Mass Air Flow (MAF) sensor measures the amount of air which passes through it into the engine. The PCM uses the mass air flow information to monitor engine operating conditions for fuel delivery calculations. A large quantity of air entering the engine indicates an acceleration or high load situation, while a small quantity of air indicates deceleration or idle.

The MAF sensor produces a frequency signal which can be monitored using a scan tool. The frequency will vary within a range of around 2000 Hertz at idle to near 10,000 Hertz at maximum engine load.

DTC P0101 will be set if the signal from the MAF sensor does not match a predicted value based on barometric pressure, air density, manifold pressure, throttle position and engine RPM.

CONDITIONS FOR RUNNING THE DTC
^ The engine is running.
^ Ignition voltage between 9.0 and 18.0 volts.
^ Throttle is steady and less than 30 percent.
^ EGR duty cycle is less than 100 percent.
^ EGR pintle position is less than 100 percent.
^ MAP is steady and less than 80 kPa.
^ EVAP canister purge is less than 100 percent.

CONDITIONS FOR SETTING THE DTC
The difference between actual airflow and predicted airflow is more than a calibrated value.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
Inspect for the following:
^ Skewed or stuck TP sensor. A faulty TP sensor or TP sensor circuit can cause the PCM to incorrectly calculate the predicted mass air flow value. Observe throttle angle with the throttle closed. If the throttle angle reading is not 0 percent, test for the following conditions and repair as necessary:
^ If none of the above conditions are noted and the throttle angle reading at closed throttle is not 0 percent, replace the TP sensor.
^ Skewed MAP sensor. A skewed MAP sensor can cause the BARO reading to be incorrectly calculated. To test the MAP sensor, compare the MAP/BARO reading on the vehicle being diagnosed to the MAP/BARO reading on a normally operating vehicle. If a large difference is noted replace the MAP sensor.
^ Plugged intake air duct or dirty air filter element.
^ The actual mass air flow is compared to a calculated Mass Air Flow based on the MAP, TP, and engine RPM readings (speed density). A skewed/unresponsive MAP sensor at key ON will cause the calculated mass air flow value to be inaccurate. When the engine is started a calculated difference between actual Mass Air Flow and Calculated mass air flow occurs. DTC P0101 will set, the vehicle will stall, a default mass air flow based on the MAP sensor will occur. Because the MAP sensor is skewed/unresponsive the default mass air flow values are incorrect and vehicle may not restart. If a fault occurs which causes the MAP sensor value to be incorrect (poor vacuum connections, damaged vacuum source, or defective vacuum hoses, air entering the engine without passing through the MAF), DTC P0101 will set and the default mass airflow value will be substituted. Because the MAP sensor value is incorrect the vehicle may not start and run.

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection.
Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Diagrams.
^ Damaged harness.
Inspect the wiring harness for damage. If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display may indicate the location of the fault. Refer to Wiring Repairs in Diagrams.
^ Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION

The numbers below refer to the step numbers on the diagnostic table:
3. Only, if sent here from the Engine Cranks But Does Not Run, continue to follow diagnostic table even if DTC P0101 has NOT failed this ignition.
4. This step tests the MAP sensor. By disconnecting the MAF sensor, the vehicle is forced into speed density. Speed density is based on the MAP, TP, and engine RPM readings. With a skewed/unresponsive MAP sensor, the speed density calculation is incorrect and vehicle may not start. For further information refer to diagnostic aids.
5. This step tests for skewed or sticking MAP sensor. MAP sensor should respond smoothly and gradually as RPM is increased. Compare MAP sensor of affected vehicle to that of a normally operating vehicle if a large difference is noted replace the MAP sensor.
9. Verifies that ignition feed voltage and a good ground are available at the MAF sensor.

 

[JDHedman]

hope this helps ya

 

[smug]

If it is blowing the fuse I would trace the pink wire from the fuse box up to the sensors and see if you can find a short.

 

[DOC-Z]

Thanks JD, but according to the test discription, I can't get past step #2. Still, I was looking for that info online and couldn't find that at all.

SMUG: Pink, wire...got it.

Also, I was just under the car and noticed there is not a 3rd O2 sensor. I could have sworn the GTP had a 3rd, but I'm not positive. I do know a lot of guys on the forums deleted an O2 sensor, but I'm not sure which one. I have to replace the "Y" pipe anyway (NOTE: the crease on the left hand side of the shot, where the drivers side pipe bends to join the passenger side), but I think this is wrong:

 

[Jfrost]

GTP's have two O2 sensors, one on the rear manifold and one right after the catalytic converter.

 

[10sec]

Have you tried replacing the MAF? A bad maf can continue blowing the fuse over and over and over. James will eventually pop in here, he's good at troubleshooting 3800's. I would try the maf though, pretty sure i've seen this problem before.

 

[DOC-Z]

Have you tried replacing the MAF? A bad maf can continue blowing the fuse over and over and over. James will eventually pop in here, he's good at troubleshooting 3800's. I would try the maf though, pretty sure i've seen this problem before.

Yesterday night I was talking to a local mechanic who said the same thing. I bit the bullet and bought a new MAF to the tune of $160 (minus the core) and it did nothing. Codes are exactly the same.

GTP's have two O2 sensors, one on the rear manifold and one right after the catalytic converter.

I have an L26 Firebird, not a L67 GTP. However, there is not a sensor after the catalytic converter, just the bolt in the bung BEFORE the cat.

 

[KagA152]

there should be an o2 sensor after the cat, im not familiar with the f-body 3800, so there could be just 1 in the y pipe or two (one for each bank). i will also agree you problem is most likely in the pink wire. replace the fuse then trace that wire and shake the harness and watch the fuse to blow, youll be close to the short

 

[DOC-Z]

I've been F***IN' with this light for months now.

I checked all of the connections at the fuse panels, with nothing showing up. Upon checking all of the ground wires, I found one which was completely disintegrated. Made a new one, pulled & replaced the fuse, re-set the computer.....NOTHING!

I was told to check the wires at the PCM by a local mechanic friend. He said 3800 F-Bodies have a problem with ground wires coming loose there. Checked it, none were loose. All grounds were fine.

The exhaust was pretty much falling off. The old one was hacked and pieced together by a blind man with a broken arm. I put on a SLP loudmouth and replaced the rear O2 sensor. I pulled & replaced the fuse, re-set the computer and the check engine light stayed off for 25 - 30 starts!

WOOT WOOT!

Then I took the car for a drive and the check engine light flashed a few tiimes, then turned off. Then it flashed again and turned off. Then it flashed again (for the third time) and it went off and stayed off. Upon re-starting the car, the D@** light went on again.

So, why would the check engine light flash?

 

[Eagle]

flashes for multi-misfires...

coilpack issues?

 

[DOC-Z]

The front spark plug on the drivers side was loose.

 

[RICH17]

Hopefully it fixes it

 

[DOC-Z]

I think I have the initial problem licked. Fingers crossed!!!