evap problem

Well it finally threw a "check engine" I've done everything to this sick 97 LS 4x4
it has 137K, Ignition switch, Lower Intake, all the suspension stuff shocks ball joints, I've read all the blazer threads and can honestly say every one of them I have learned something. I don't know where to start with this one, the thing runs great but I have thrown a code and PepBoys says it has a "small" Evap leak. I do know to click my gas cap! where the hell do I start with this one, and do I have to disconnect the negative terminal and clear the codes every time I try to trouble shoot this thing ?

It runs great and I have 10 months until I have to worry about a NYS inspection. I Just like this rig and I want to keep it running nice.

thanks
Jkdon

I've got the same thing going on with my '99 Jimmy. Every couple of tanks or so the CE light comes on for 15 or 20 miles and then goes off. My garage checked the codes same diagnosis, "small evap leak". Sometimes it goes 3 or 4 tanks of gas without coming on. Now it is on for the second night in a row. For $10 I'm gonna try a new cap.

yea

I was hoping to try a new cap myself, does anyone know where else to check maybe a purge canister or possibly vacum lines. I'm thinking this one might be a nightmare to troubleshoot.

Jkdon

I had this this problem for a while cuse I had a cracked gas cap. I replaced the cap and kept getting the code. One day I was in a bad mood and clicked the cap like 4 or 5 times and the light went out he next day and stayed off. Who knows if it was the exessive cliking or not but I'll take it!

I'm seeing the same thing. If I click the cap half a dozen times and kinda bind it sideways as I turn it, to make it tighter, it will not throw the light...maybe. I can't get it down to exactly what works and what doesn't. Gonna replace the cap in the morning.

The DTC, (diagnostic trouble code) you are getting checks for leaks in the evaporative fuel system. This includes the fuel tank, fuel filler neck, fuel cap, purge canister, purge control solenoid, and all of the lines that connect them together. You will be looking for a leak that is .020 or smaller. This can be quite difficult to locate and may require the use of a smoke machine, (an expensive piece of test equipment that a good shop should have).

With OBDII equipped vehicles, (1996 and newer) the DTC's must be cleared with a scan tool, simply disconnecting the battery will not clear them.

i have the same problem on my 1996 i replaced the cap jwith a staint and it came back

well pulled the neg terminal and cleared the codes, the light went off for about a day and just came back on. I've replaced the cap and looked for the obvious but nothing. This smoke machine might be my only option, I can't believe all the little problems I've taken care of on this thing and I'm dealing with this. I have never had to break down and bring it into a shop and I've owned the truck for 7 years. I noticed the evap service port under the hood and then some type of sensor that attaches to the intake. Maybe start there right? Is there any type of charged canister that can attach to that port kind of like a smoke machine, or did I just think of the next product that will be on the autozone shelves? Crazy, I can't think of any other way to trouble shoot this thing.

thanks
Jkdon

well pulled the neg terminal and cleared the codes, the light went off for about a day and just came back on. I've replaced the cap and looked for the obvious but nothing. This smoke machine might be my only option, I can't believe all the little problems I've taken care of on this thing and I'm dealing with this. I have never had to break down and bring it into a shop and I've owned the truck for 7 years. I noticed the evap service port under the hood and then some type of sensor that attaches to the intake. Maybe start there right? Is there any type of charged canister that can attach to that port kind of like a smoke machine, or did I just think of the next product that will be on the autozone shelves? Crazy, I can't think of any other way to trouble shoot this thing.

thanks
Jkdon

On an OBDII system like yours, pulling the negative cable does not clear the codes. It must be done with a scanner.

The green service port next to the sensor is for testing the EVAP system. The sensor you are referring to on the plenum is the canister purge solenoid. The EVAP system uses that solenoid for two things: When the EVAP monitor is run, it opens and allows a predetermined amount of vacuum to build up in the tank, lines, and purge canister, then it closes. There is a sensor on the top of the fuel tank that monitors the pressure, (both negative and positive). If there is excessive pressure loss within a certain time period, there is a leak, and the "SES" light turns on. The other purpose of the canister purge solenoid is as the name implies. Within certain parameters, the solenoid will open, along with another solenoid near the purge canister itself, and the fuel vapors that were stored in the canister are routed to the intake manifold and burned. Pressurized smoke in a can, haven't seen it, yet.

I understand the fact that the light is off doesn't clear the code stored in the memory. Can someone tell me why the light will come and go, on and off 2 or 3 times sometimes, in the 50 mile trip to or from work? Sometimes it will be off for a week straight then come back.

My 99 Blazer had the same problem. It was the purge solenoid behind the gas tank, and in front of the spare tire(tire has to be remove to change solenoid).

There are some circuits that are monitored continuously. If there is a fault, it will turn the light on and it will remain on until it is manually cleared. These are called "DTC type A" faults. Some circuits are monitored only under certain driving conditions, or "parameters" that must be met for the test to run. When one of these circuits has a fault, the light will come on and remain on until the monitor runs again. If the fault is not present, it will turn the light off. These are called "DTC type B" faults. Each monitor has its own unique parameter. Type "A" faults are more serious than type "B" faults and require immediate attention, that's why the light stays on with an "A" fault. Hope this helps.

Well I pulled the "plug" and the light has not come back on since. My SES light never came on before, so I imagine this is a type A fault code? should still probably find out how much for a smoke machine test right?

thanks
Jkdon

You're right, P0442 is technically a type "A" fault code. However, when it comes to the SES light, it behaves as a type "B" fault code, meaning it will turn the light off provided it passes the next test. The reason it was programmed that way was for a little "forgiveness" if you forget to tighten your fuel cap.