Engine Check Light On

[clay]

I have a 2001 cavalier and the engine check light has started staying on all the time. I have checked the cng fuse and it is good but when I pull it and start the car the engine light is not on? I have looked at the wiring and everything seems to be plugged tightly together. What else might it be?

Thanks Clay

[freedml]

Re: Engine Check Light On

You should start by reading the codes. Inexpensive readers are available at most auto parts stores. You can get one that resets the light. Write down the codes, reset it, and see how quickly it happens again.

[clay]

Re: Engine Check Light On

Ok, thank you I'll give it a try

[kirkbenge]

Re: Engine Check Light On

How long has it been on? When did it start? Do you have any trouble starting in natural gas mode?

I've discovered that my '01 cavalier will get a check engine light if I don't crank for a full six seconds when I start it, if it then starts on gasoline. If I stop cranking just before it starts, and then have to re-try, mine will always start in gasoline mode, and if it does, the check engine light will come on and stay on for 2 to 3 days. (I don't know what resets the light, whether I need to drive a certain number of miles, or whether I need to start on CNG with no problems a certain number of times)

Would this describe your problem? or has your light been on for longer with no false starts??

KIRK

[clay]

Re: Engine Check Light On

In reply, yes I have used an OBDII scan tool to read the codes in the computer and the only code that I could get was P1202 ? Now this scan tool does not have a code difinition for P1202 it says that the first digit should always be a 0 ? I'm not sure what to make of that. I am how ever only getting the error code or engine light when I have the cng fuse plugged in. I can not get the car to start in cng mode. I allow the key to be on for a number of seconds befor I engage the starter. Right after it starts, with the red light on the fuel switch out, I can hear a click noise from some where in the engine compartment and then the red light comes on the fuel switch and the check engine light come on, all in about 3-4 seconds?
I have pulled all the fuses and checked them, I have checked all of the power cables and plugs to make sure they are all tight.
Also as resent history I have just changed out the HPR becouse I was getting a backfire out of it. After I changed that the car worked just fine for two times that it was started and then this other problem happened.
I'm figuring that it must be within the cng system because that is when I'm getting the lights on but I don't know what else to look for?

If any one has had this type of problem before please advise me on what to do next, Thank you all.

[siai47]

Re: Engine Check Light On

P1202 refers to "gas mass sensor circuit low frequency". The car is starting in GNG mode but the sensor isn't reading the flow correctly. I suppose that the click you hear under the hood is the ECU shutting off the fuel at the low pressure lockout valve and then setting the DTC you are recording. The gas mass sensor is the square looking thingy just downstream of the low pressure regulator. It provides feedback to the ECU about gas flow so the ECU can operate the servomotor butterfly valve (also located in this unit) to provide the proper mixture to the engine. I know you said that you checked the wires, but you should pull and check the connector going into unit. There is a red plastic lock on the bottom of the connnector that needs to be removed before the connector can be released from the unit. check the pins in the unit and the connector for corrosion. With a light look inside the unit and make sure there is no moisture inside. If it still isn't working, check the treads on this site about how to repair or clean it.

[krnorth]

Re: Engine Check Light On

I had a similar problem with my 2000 Cavalier. It would get a check engine light and when we would reset the computer the light would eventually trigger and come back on. There were TWO reasons this was occuring.

First we had a leak on the LPL, we replaced that for about 80.00. This still did not fix the problem.

The second problem was a leak from the regulator. We purchased the rebuild kit for about 120.00 or so and once we had both of these replaced my check engine light nightmare was done wtih. The MASS GASS SENSOR has to have a very TIGHT range of gas flowing properly otherwise you will get a check engine light, and thus any loss of pressure or flow of gas due to a leak or whatever causes this problem.

Someone else on here once said they unplugged the computer or maybe the battery to the car for 24 hours and that cleared all their problems with check engine lights and such. *shrugs*.

[clay]

Re: Engine Check Light On

Update; I have done as suggeted and I inspected the wires going into the mass gas sensor. I found no moiture or corrosion within?
I cannot smell or hear any other leaks within the system either.
My engine light does come on still a couple of seconds after the car is started. Once reset (each time) I turn the key to on and I have no red light on the fuel switch and the gas gage reads the pressure from my cng tank untill the engine light come on then it reads the gasoline tank.
I still am at a loss, I don't know if I should dig into the mass gas sensor or not?

[clay]

Re: Engine Check Light On Updated info

I have good news, a least I think so. I pulled the top of the MGS and found a burnt ?????? on the top of the circut board. Its possision number is R13? it is just to the right of the flexable band that holds both boards together. Its black and its about 1/4 inch square. It scortched the MGS cover plate. It looks to me to be cracked and the soldering was all burnt and it has left carbon covering about a 1 inch area of the circut board from its arching.

Question 1: Does anyone have info regaurding what this part is and where I could purchase a new one.

Question 2: Does anyone have experience in doing this kind of soldering repair that could coach me throught it?

[krnorth]

Re: Engine Check Light On

That's not necessarily GOOD NEWS.

Some people have cleaned up and resoldered their connections and had succesful repairs.

Others will end up paying the nearly 1600.00 it costs to purchase that part...yes, you read it right, that's what they COST! (ridiculous indeed)

[freedml]

Re: Engine Check Light On

"R13" indicates resistor number 13, but I would guess from the description that it's more likely to be a voltage regulator. Those are more likely to burn up on their own than resistors anyway.

[freedml]

Re: Engine Check Light On

$1600 doesn't surprise me. That's about the cost of several CNG parts for the GX. The fuel sender and the HPR cost that much or more off the top of my head. Their parts pricing formula is designed for things they sell hundreds of, not parts they sell one at a time. When my HPR went out they had to ship one from Japan -- apparently none left in the US.

[siai47]

Re: Engine Check Light On

When I go into town tomorrow, I'll take a look at the "spare" that I have and see if I can get a number off the part that is burned up in your gas mass sensor. I bought the whole NG assembly that is located on the top of the engine (LPR, LPR lockout, gas mass sensor, gas distribution assembly, wiring and mount) for $600 on E-bay a few months ago. You might check there every once and a while if yours can't be fixed.

[siai47]

Re: Engine Check Light On

O.K.--it's tomorrow but I can't be of much help. I took the cover off of my spare and found R13. Looks like it is just a surface mount resistor of a fairly high wattage rating for a surface mount. On the unit I took apart, there was no evidence of any heating around the resistor. The conformal coating was all intact and no evidence of heat on the cover above it. Unfortunately, there was also no marking of any kind on the resistor to determine what resistance it is . I wouldn't trust checking the resistance with an ohm meter because it is in the circuit and would most likely give a false reading. However, I would try contacting Impco service, give them the part number of the board and the component number and see if someone there will tell you what the resistance is. It would also be nice if they could tell you what circuits are powered through R13 and if this component has been a problem in the past. The fact that the resistor overheated for a period of time before it failed (evidence the charring on the cover) would lead you to believe that something it powers either internally or externally is overloading it. If you can find out the resistance and wattage of R13, it looks like you could fit a standard resistor (not surface mount) in its place to see if you can get this thing working. Best of luck

[clay]

Re: Engine Check Light On

Thank you everybody for your help
I have talked to Impco and they claim no info because this system is now owned by Quantum. I've also talked with their tech and had no luck with them either! ( don't waist your time trying ) All info has to come from GM and I'm still waiting for their reply but I don't have much hope
I'm still trying to hook up with a computer board tech that is a friend of my brother. Maybe I'll have more news after that!
In the mean time if anyone has a set of used boards that they are thinking of parting with let me know please.