99 suburban service engine light

[no_h20]

My service engine light has been coming on intermittently over the past 2 years. I have changed plugs, wires, o2 sensors, had the fuel injection system cleaned, etc. Sometimes the code is the o2 sensor and other times it is mis-fires. I have not tried to replace the cam sensor as some have suggested.
Also, my coolant reservoir is always empty althought the radiator does not ever seem to be lower than ~ 1 - 1 1/2 inches below the cap.
Is it possible that the 2 are related?

[gregory914]

My 97 Burb w/115K miles did the same thing with the SES light until it stayed on all the time and I did have a mis-fire code. I you take it to a place with a scanner or even Autozone they can get the code number and tell you what it means.

If it is a P 1345 code you need to read my thread with that title further down this page. The cam position sensor is telling you the timing is out of tolerance and it is probably because your distributor gear is worn. You can try to set the timing but it will come back on soon. the only way to set the timing is with a GM compatable scan tool, not the little cheap ones either, the engine timing advance and retard is checked while varying the RPMs and you only have a 2/4 degree window to adjust. If your truck is up in miles it's more than likely the distributor gear. Don't chase this problem, the gear is only $40 at the dealer and find the proper scanner to have the timing set and you'll be good for another 100K miles.

The coolant should be right up to the top when you take the cap off with it stone cold if it's not ,you have a leak, and that's why the reservoir is always empty.The coolant being low is probably not related to the SES light but the fix is! The intake manifold gasket may be leaking into the crankcase at a very small amount not noticable in your oil (milky brown). These gaskets are notorious for leaks on this vintage engine and typicaly go bad from the factory at 60K miles or so. But first check your radiator and water pump for any signs of leakage.

The GOOD news is that when you replace the intake gasket you have to remove the distributor and you can put the new gear on at the same time! But you have to have the timing set at a place that has the correct scan tool and Software.

This Forum is great but I've seen too many people replacing sensors and all kinds of other things that don't get to the root of the actual problem and cost tons of $money. One good/bad thing about these Suurbans or GMs in general is that they ALL seem to have the exact same problems at some time in their life span, and those of us who have lived through them can help those experiencing these problems for the first time. Like; fuel pumps, idler arms, blower motors, rear diffs, BRAKES, door actuators, AC Freon leaks from rear evaporater and last but not least the intake manifold/ mis-fire up hill/SES light/ Timing off issue.

[GMMerlin]

Well before you replace any more parts, have you had the codes pulled?
Lets start with some diagnostics before you go and spend money on parts that may or may not address the problem.
You say its O2 sensor codes or misfire codes...which ones?
There are a number of codes for the O2 sensors that will lead in other directions other than replacing the sensors.
With the misfires are you experiancing any symptoms?
As far as your coolant leak goes, have you had the cooling system pressure tested?

[no_h20]

Originally Posted by GMMerlin

Well before you replace any more parts, have you had the codes pulled?
Lets start with some diagnostics before you go and spend money on parts that may or may not address the problem.
You say its O2 sensor codes or misfire codes...which ones?
There are a number of codes for the O2 sensors that will lead in other directions other than replacing the sensors.
With the misfires are you experiancing any symptoms?
As far as your coolant leak goes, have you had the cooling system pressure tested?

I have had the codes pulled. I have been having problems over the last 2 years. Usually it has been misfires, but the last time it was an O2 sensor. I replaced the sensor and the code is now off. The intent of my question is could I be getting a leak that causes O2 sensors to go bad or cause misfires? My mechanic has also replaced O2 sensors as well.

I have never had the cooling system pressure tested. What type of equipment is required to do this? Can most mechanics do it? The part that I don't understand (if I have a intake gasket or other internal leak) is that the coolant level is never below 1 to 1 1/2 inches below the filler and the overflow bottle is always empty (after a weeks time or so). I never find any coolant puddles on the ground.

[GMMerlin]

On those vehicles you usually dont have a coolant leak that will cause a misfire or O2 sensor codes.
Now any TECHNICIAN worth his stuff will have the tools to properly check a cooling system for leaks and will know the areas to look at.
Your cooling system should never go low..if it does, there is a leak. I would guess on that model that the intake is the source of the leak.
(You will notice that I do not give definate diagnostic answers because I am not looking at your vehicle, but I will give general ideas..I would shy away from anyone on a forum that says that XXX is definately your problem)
As far as misfires go, you did not answer my question...are you having any symptoms or just the SES light is coming on and a misfire code is retrieved?
The reason for this is there are a couple things that could be going on that will cause a misfire code and a misfire not being felt by the driver.
These codes do not just happen for no reason and some diagnosis needs to be done to find the root cause of the concern...the diagnosis starts with your description of what was going on when the SES light was illuminated and then some circuit testing to determine the failure.
There are many MECHANICS that will replace a part because a code was set..a TECHNICIAN will perform extensive DIAGNOSIS to determine the root cause of the failure. (Many times a componant is not the root cause, but the effect of what happened)

[no_h20]

Originally Posted by GMMerlin

On those vehicles you usually dont have a coolant leak that will cause a misfire or O2 sensor codes.
Now any TECHNICIAN worth his stuff will have the tools to properly check a cooling system for leaks and will know the areas to look at.
Your cooling system should never go low..if it does, there is a leak. I would guess on that model that the intake is the source of the leak.
(You will notice that I do not give definate diagnostic answers because I am not looking at your vehicle, but I will give general ideas..I would shy away from anyone on a forum that says that XXX is definately your problem)
As far as misfires go, you did not answer my question...are you having any symptoms or just the SES light is coming on and a misfire code is retrieved?
The reason for this is there are a couple things that could be going on that will cause a misfire code and a misfire not being felt by the driver.
These codes do not just happen for no reason and some diagnosis needs to be done to find the root cause of the concern...the diagnosis starts with your description of what was going on when the SES light was illuminated and then some circuit testing to determine the failure.
There are many MECHANICS that will replace a part because a code was set..a TECHNICIAN will perform extensive DIAGNOSIS to determine the root cause of the failure. (Many times a componant is not the root cause, but the effect of what happened)

Thanks for the info. I have felt misfiring on the engine, but not consistantly. I have felt it much much less since the fuel injection system has been cleaned.

[no_h20]

I did a pressure check on the radiator and its leaking. I think it is leaking at the rear of the intake gasket. I guess I have to get that fixed now too......