Puzzling check engine light

Good evening everyone,
I have a 2001 Isuzu Trooper that has had the check engine light come on on three different occasions. The first time was when I installed Bosch spark plugs. On the second and third time the intake manifold gasket had failed on the Trooper.

Today the check engine light came on again. Frankly, I am completely stumped as to what the cause might be this time. I ran Auto-rx in the engine right after the intake manifold gasket was replaced for the second time. I then re-installed Amsoil's bypass unit and Series 3000 oil in the engine. All this happened about 15,000 miles ago.

Lube Control's FP60 has been used in every tankful of gasoline since the gasket failure.

Like I said, the check engine light just came on and stayed on with no warning. The light does not blink at all. The engine does not shudder at idle, it does not run rough, there are no rpm surges, and there is no hesitation when I step on the gas pedal. The engine does not spit or misfire. The engine is operating so smoothly as matter of fact that I am baffled at to what the cause might be.

The egr valve was cleaned about 18,000 miles ago. The pcv valve was checked at the same time.

Starting early this spring, the engine starting pinging under moderate acceleration even with premium fuel. It got so bad that I finally switched away from the fuel I had been using(Shell's 93 octane) and went with BP's premium. The pinging stopped and hasn't been back since. I switched gasoline brands about 1500 miles ago. Could this change have triggered something? What about my running premium fuel in the Trooper? Could how the fuel is burning trigger a check engine light?

What about an electrical issue? Could the alternator or battery not functioning properly trigger a steady check engine light?

Has anybody had an issue with the check engine coming on and staying on?
My vehicle is a 2001 Isuzu Trooper with about 92,000 mile on the odometer.

Thanks,
Bobby

If you have an autozone in the area they will read the CEL codes for free. Otherwise we would just be guessing what your issue is.

-Ryan

I don't think the 98+yrs on the Trooper or Rodeo like the Bosch plugs.

I had Bosch on my '97 Rodeo for almost 75k miles - they were rated 100k plugs, I will NEVER again use them. Truck ran ok with them, but after switching to NGK plugs, there's a big difference - not just because they were new, but the pinging that you're referring to, I used to have that on mild uphill inclines with the Bosch plugs.

Haven't had that since changing to NGK plugs.

FWIW - I've had two Rodeo's and the ONLY two things I would use Bosch for on an Isuzu is the O2 sensors (Bosch is actually VERY good here) and the Bosch alternator, that's it.

keep runnig BOSH and you will find out how expensive a catalytic convertor is
you really neeed to get those out of your engine you may be able to use them as fishing weights as the are no good for automotive use get either nippendenso plugs or ngk

Sorry for taking so long to get back to everyone here. The same weekend I posted this question, I popped open my hood and discovered battery acid leaking down the sides of Trooper's battery. Thinking that the check engine light could be tied to faulty battery(I bought it about eight months ago.), I replaced the battery. Everything was fine until about a week ago when the check engine light came on again.:frown: This time I bought a code reader from Sears and read the codes. It was P0401 and the reader also stated "Insufficient EGR flow."

I cleaned out the valve and sprayed about half a can of Amsoil's Powerfoam down the EGR's intake(smaller hole) about two days ago. Last night the check engine light came on and again it was the same code.:banghead: Is there something more I need to do to solve this problem or did I not spray enough cleaner down the EGR's intake? In doing searches, I think I ran across references to using a coat hanger and reaming out something by the EGR valve. If this would apply to my situation, please enlighten me. The Trooper does run better, however, the check engine light is on.

By the way, the times the check engine light came on for the spark plugs and IMG were resolved quite a while ago and are not an issue in this case. Sorry for the confusion.

Thanks,
Bobby

Maybe this will help. It is kind of technical and needs a Tech 2 to run the tests, but some items can be done by you. Never stick anything into a passage unless you are sure you can remove it without breaking it if it gets stuck. Good luck



2001 Isuzu Truck Trooper LTD 4WD V6-3.5L



Steps 1 - 5http://library.alldatapro.com/alldata/LIB~C35748~R0~OB0~P4R0H~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34858149/34858245/84059278/91175492/91175494Steps 6 - 10http://library.alldatapro.com/alldata/LIB~C35748~R0~OB0~P4R0H~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34858149/34858245/84059278/91175492/91175495


Circuit Description
The powertrain control module (PCM) tests the exhaust gas recirculation (EGR) system during deceleration by momentarily commanding the EGR valve (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34872079) to open while monitoring the manifold absolute pressure (MAP) sensor (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857030/34857526) signal. When the EGR valve is opened, the PCM (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857030/101367125) monitors the change in MAP (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857030/34857526) input signal. The PCM compares the MAP change to a RPM vs. BARO table. When the PCM interprets the change in MAP to be out of limits, the PCM will set DTC P0401. The number of test samples required to accomplish this may vary according to the severity of the detected flow error.
Normally, the PCM (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857030/101367125) will only allow one EGR (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34858149) flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows twelve test samples during the first ignition cycle following a Tech 2 "Clear Info" or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.



Diagnostic Aids
Check for the following conditions:

Poor connection or damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the Actual EGR (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34858149) Position display on the Tech 2 while moving connectors and wiring harnesses related to the EGR valve (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34872079). A change in the display will indicate the location of the fault.
Ensure EGR valve (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34872079) is correctly mounted. See On-Vehicle Service.Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

NOTE: If the EGR valve (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34872079) shows signs of excessive heat, check the exhaust system for blockage (possibly a plugged catalytic converter (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34856671)) using the "Restricted Exhaust System Check".

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart:

A malfunctioning MAP sensor (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857030/34857526) can set an EGR (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857699/34858149) DTC. The MAP sensor could send a constant signal which is not low enough to set a low MAP (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/80851247/83266461/83266477/83266480/34853741/34857029/34857030/34857526) DTC. The constant signal from the MAP sensor also may not be high enough to set a high MAP DTC. This step verifies that the MAP sensor is responding.