Any GM service techs?

smooth

smooth

Club Member
I have a haunting P300 code and also P200 code (sometimes a random lean o2 code due to misfire I imagine) on my Denali, changed plugs, wires, coil packs, had injectors flushed. Before this code I changed knock sensors and harness, no problems for about 3 months. Within the last 9 months replaced alternator, battery and fuel pump with float. Took the truck into a shop they did a smoke test because they claimed intake leak, didn't work out for them. They decided to refer me to a dealership, I do t wanna spend 1500 chasing this code I will just sell the truck.

Any advice would be much appreciated
 
2002 Denali, 6.0 with 112k miles

I will also add this is very random, truck will run nice and smooth when cold sometimes the it will just run very rough. The CEL will come on then go off then sometimes come on and blink
 
Last edited:
check fuel pressure go from there. With the p0200 codes possibly a wiring issue do you have several cylinders missing or just one?
 
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Ya if it was a ford it would just blow the spark plugs out when the coil goes bad, its much cheaper to change out a cylinder head than a wire harness lol.
 
Flashing MIL usually means a misfire, or something that is damaging the cat.
I've had them where the valves don't seal and it causes a light, but if its running fine, this could be a computer programming issue and its tossing false codes. Could also be that the computer is failing, which is often easily diagnosed by tapping on it with a screwdriver handle.
 
Grab the harness while its running and wiggle it try to follow it all the way to the computer. Look to see if it changes any way it runs when u shake it. That quick way to check for a busted wire in the harness.

Im not sure on GM but i know on Chryslers if there is a miss detected the computer will kill the injector to that cylinder wich could be why that p0200 code shows up but dont quote me on that one.

Id still check the fuel pressure if it hasn't been done recently you have many symtoms of a bad pump or clogged filter, etc
 
smooth said:
yea the shop told me, it was one side only. I will have to call and ask again
Click to expand...
If it's one side only, I'd be looking for a bad power or ground in the injector harness. IIRC, the injectors are all fed +12V off one leads, and each injector is grounded through the PCM to fire. Maybe run a noid light on one of the pink wires on an injector and see if you can seen it flicker.

Weak fuel pressure is another possibility as is a failing MAP sensor.
 
Intake gasket leaks can usually be confirmed by monitoring O2 and fuel trim data. Obviously if one side is leaking, there will be much higher LTFTs than the other bank.
 
The following diagnosis might be helpful if the vehicle exhibits the
symptom(s) described in this PI.

<dl>
<dt><a id="d1224e95">Condition/Concern</dt>
<dd>
DTC P0300 Setting After engine Repairs.

It is possible to have injector connectors crossed for cylinder 5-7 and
6-8 to cause an engine misfire.

The engine misfire may not be detected and may happen during
deceleration.
</dd></dl>
<dl>
<dt><a id="d1224e110">Recommendation/Instructions</dt>
<dd>
If you have determined crossed injector connectors maybe a possible case, use
the applicable SI document to validate the injector connector routing.

Correct the injector connector routing and evaluate for the concern.
</dd></dl>
 
smooth said:
I have a haunting P300 code and also P200 code (sometimes a random lean o2 code due to misfire I imagine) on my Denali, changed plugs, wires, coil packs, had injectors flushed. Before this code I changed knock sensors and harness, no problems for about 3 months. Within the last 9 months replaced alternator, battery and fuel pump with float. Took the truck into a shop they did a smoke test because they claimed intake leak, didn't work out for them. They decided to refer me to a dealership, I do t wanna spend 1500 chasing this code I will just sell the truck.

Any advice would be much appreciated
Click to expand...
A Misfire won't cause a lean code. misfire=unburned fuel = rich, not lean. More stuff---Inspect the following items:


  • Inspect the vacuum hoses for splits, kinks, and the correct connections.
    Refer to Emission Hose
    Routing Diagram    .
  • Inspect throttle body and the intake manifold for vacuum leaks.
  • Inspect the crankcase ventilation system for any vacuum leaks .
  • Verify the PCM grounds are clean and secure. Refer to Ground
    Distribution Schematics     in Wiring Systems.
  • Inspect the ignition coil ground circuit for an open on the cylinders that
    are showing misfires. An open ground causes all 4 ignition coils to be
    inoperative. The Misfire Current counters only display 2–3 cylinders misfiring,
    not all four cylinders.
  • Verify that all of the injector harness connectors are connected to the
    proper injector
  • Inspect the injector fuses and the ignition control fuses. If you find an
    open fuse, locate and repair the short circuit. Refer to Wiring
    Repairs     in Wiring Systems.
  • Test for incorrect fuel pressure and for a restricted fuel flow. Refer to Fuel System
    Diagnosis    .
  • Inspect for a restricted exhaust. Refer to Restricted
    Exhaust     in Engine Exhaust.
  • Test for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel
    Diagnosis    .
  • Refer to Base Engine
    Misfire with Abnormal Internal Lower Engine Noises     in Engine Mechanical
    4.8L, 5.3L, 6.0L if an abnormal engine mechanical noise is heard.
 
Thank you for all the info, I'm going to dig into these suggestions. Just gonna buy a new truck in the mean time, I hate to sell the Denali
 
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