I was driving yesterday and get a check engine light for the first time. Manual says that if it stays on and doesn't blink that it is probably an emission problem and it is not as bad as if it was blinking. That it probably can be traced back to the the gas cap of all things. It said to resecure it and drive it for a few days and it should turn off. I did this and so far it is still on. I guess I will give it a few days. What do you guys make of this?

 

Check to see what codes you have. Here is how to do it:

The "diagnostic display" mode is entered with the following Procedure:

1) Turn on the ignition but don't start the engine.
2) Press the "reset" button to turn off any warning messages
3) Press and hold "options" and
4) While holding "options", press "fuel" four times within a 10-Second period.

Initially, the on-board diagnostics go into the "automatic" mode, which shows each module's DTCs in a
pre-set sequence: (Page No. are for the GM Service Manual)
10 PCM Power-train Control Module page 6-357 - 6-361
28 TCS Traction Control system ABS on page 5-86
?? RTD Real Time damping page 3-136
40 BCM Body Control Module page 8-405 LTD Page 8-727
60 [PC instrument Pane! Cluster page 8-508
80 radio page 8-213
99 FIVAC Heater Vent-Air Conditioning page 1-118
A0 LDCM Left Door Control module page 8-904 to 8-951
Al RDCM Right Door Control Module page 8-904 to 8-951
AC SCM Seat Control module page 8-1064-8-1082
B0 RFA Remote Function Actuation page 8-676

For each module, all DTCs will be displayed. If none are present in a module, you will see "no more codes" on the ICP display.
There are two kinds of DTCs, "Current" and "History," designated with a letter suffix, "C" or "H". A current code indicates that the malfunction is present in the system whose module is displaying data. A history code indicates a problem existed in that module sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it is possible it's evidence of a previous problem. Now solved, that was not removed by clearing codes. More likely is that a history code indicates an intermittent malfunction.

"Intermittent" are the most challenging DTCs. An intermittent may have happened only once, may have happened more than once but is inconsistent in its appearance or may be happening on a regular basis but not at the time the IPC is displaying codes. History codes can also be caused by a current malfunction in a system that is not Operating at the time DTCs are displayed. An example is the rear window defogger, which doesn't operate until the BCM detects engine rpm. For history codes set by a system that does not operate with the key on and engine off, a special diagnostic tool called a "scan tester is necessary to properly diagnose the malfunction.

Once the IPC has displayed all 11 modules, the system goes into the manual mode, which allows selection of each module, using combinations of DIC buttons. The manual mode can also be entered at any time during the automatic sequence by pressing any button except "E/M". Once the IPC displays "manual diagnostics", you may select a particular module by pressing the options button to go forward or the "trip" button to go back. Once a system is selected and a DTC is displayed, if more than one are present; press "gages" To move forward or "fuel" to go back. To exit the diagnostic mode at any time, press E/M". If you want to erase or "clear" codes, press "reset". Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory.

The instructions posted above omit one key optional detail. Intermittent codes are only current for the then-active ignition cycle. The DIC instructions say to check codes, turn the key on but do not start. This implies the engine shouldn't be running to check codes. That's absolutely, 100% wrong. You can check Codes at any time, even with the engine running, driving down the highway (not recommended, but absolutely double), which is the ONLY way you'll ever catch an intermittent code being "C".

Next time the light comes on, stop the car but don't kill the ignition. Then, check for codes and your "C" will he there for you to see!

 

Mine went on immediately after my first tank of 10% Ethenol gas. I checked the code and it was an O2 sensor. I reset the code and it went on again a week later, then went out by itself. It hasn't come on since.

Check what kind of gas you are using. Others in my club have had the same problem. Also, see if your gas mileage has gone down. Mine goes down significantly whenever I use Ethenol enhanced fuel. I try to stay away from them if possible.

 

I've got a predator tune. Should I go back to the OEM setting before doing any of this? Or better yet, can I even use the predator diagnostic program?

 

I have a Predator tune also. I check and clear codes without going back to the stock tune whenever the need arises, without any problems. Codes are codes. I don't think the tune matters.

 

 

My Check Engine light came on with a 10-P0440 code. The list I have from the Tech Tips does not list this one. Does anyone know which it is? I have a C5 Z06. I reset the codes and it has not come back on. . . yet.
Thanks, Tim

 

If in fact it was the gas cap, the engine has to cycle so many times before it will turn off. My chevy truck is 32 times. Yes that's right, turn on and off 32 times.

 

http://gearchatter.com/viewtopic1045...ab718c82a12042

 

I think GM has a secret program that randomly throws a check engine light just to screw with the driver. My light comes on at least once a month. The one time there was a problem I knew there was a problem long before the light came on. I do not check for codes anymore as it always goes away. I wonder if GM's electrical engineers were trained by Lucas.

 

My check engine light was staying on and turned out it was a bad mass air flow sensor. This was on an '03 with 16k miles. Fixed under warranty and it's as good as new. Hope you get your problem fixed!