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98 Gmc Sierra, P0452 Code

JS_GMC

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JS_GMC Enthusiast

JS_GMC

Posted
Posted

I have a 1998 GMC Sierra, 1500, 4wd, 5.7L V8. About 6 months ago, i had the code P0452 come up. The engine has 168,000 miles on it, and so i had replaced the gas cap thinking this could be the problem if it was the original cap. Since then, the light had gone off and never came back on. Now, i have the code back. I don't think its the cap, being as its only about 6 months old. Any ideas on what else could be causing this code to come on?

gregrocks89 Senior Enthusiast

gregrocks89

Posted
Posted

It indicates a low voltage problem in the Fuel Tank Pressure Sensor. What the fuel FTP sensor does is convert fuel tank absolute pressure into electrical signals and inputs the signal to the computer.

 

First thing to do is make sure the gas cap is good and tightened properly. Then check the vacuum lines and wiring at the FTPS (Location-Fuel Tank) to be sure they are good, clean and tight.

 

Barring a wiring problem it can be a bad FTPS or PCM.

  • 3 months later...
Dahammer New Member

Dahammer

Posted
Posted

I just resolved (I hope) a couple EVAP codes on a 2002 GMC Sierra 1500 4.8L 4x4 and thought my findings may help someone else here someday. The codes that I was getting were P0452, P0453, & P0446. Over the last couple weeks, I've cleared the codes 3 or 4 times. Immediately after clearing the codes, either P0453 or P0452 would come back up as pending, then set the MIL after 2 consecutive engine starts. If I drove the truck a day or 2 without resetting the single code, then the others would usually eventually pop up. I figured it was 2 separate issues with the EVAP system, since P0452 (Low) & P0453 (High) refer to the fuel tank pressure sensor, while P0446 refers to the vent valve.

 

I started out troubleshooting the P0452 & P0453 codes. The fuel tank pressure sensor is located on top of the fuel pump, which is in the top of the tank. The wiring connector connecting it to the PCM contains 3 wires (grey, black, green). I was able to unplug the connector without lowering the tank, so the first thing I did was check the voltage on grey wire. With the key on, engine off, there should be +5v on it. That was what I had, so all good there. Next I checked the black wire, which is ground, by ohming it out to the rail. All was good there, so I knew I had a good ground. Next I checked for a short between any of the wires with it unplugged. I didn't find a short. So I plugged it back up, crawled under the truck, reached over the top of the tank from the inside and pulled the wiring harness down a little so I could get at it to probe the wires. There are 2 grey wires in the harness, the smaller diameter one is the one to the sensor. I again checked the voltage on the grey wire and found 5v. So I took the gas cap off and checked the voltage on the green wire. With the cap off (no pressure & no vacuum), there should be approximately 1.5v on the green wire. I had 1.49v, so close enough. Next I put the cap back on and started the cold engine. When the engine is cold, the PCM runs a test on the EVAP system shortly after startup. So I got back under the truck and checked the voltage on the green wire. It was still at 1.5v, so I knew the test hadn't run yet. I just lay there with the multimeter connected for a few minutes and watched reading. The information I have says that when the PCM pulls a vacuum on the system for the test, the voltage on the green wire should be about 4.5v with a 14 in-Hg vacuum. After a couple minutes, the voltage on the green wire dropped to 0.06v. I checked it a couple times to ensure I still had a good connection to the multimeter and it stayed at 0.06v. So I checked the MIL and sure enough it was back on. I pulled the code and had P0452 (low). At this point, I figured the sensor was bad, especially since sometimes it would set P0453 first, others P0452. So I dropped the tank and replaced the sensor.

 

I also took out the vent valve and blew it out with air. There was a little dust in it, but not much. The valve also seemed the open and close fine. But I decided to spray it inside it with throttle body cleaner, just to be sure it was clean. Once it dried it, I connected it to the battery (white wire is ground, pink wire is 12v) and it closed off fine. I decided not to replace it with the updated version, since it's not that big a deal to get it out and the truck never sees anything other than pavement except for a gravel driveway. Hopefully, the cleaning cured intermediate the P0446 code.

 

Anyway, total repair took about 4 hours, including the time to clean up afterwards. The codes have not come back, where they were setting immediately after clearing them, so hopefully it's fixed. I could have saved a good bit of time if I would have had a scanner that could read the voltage and vacuum readings from the EVAP system. Unfortunately, my Actron 9180 which does read live data, could not see that data.

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