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Discussion Starter #1
Just changed my fuel pump, was having issues with the car dying when trying to go fast. Since changing that, now the throttle doesn't work. Or rather, u pump the gas and get absolutely no response. The engine starts, idles fine. But won't move. Checked and changed the APP sensor, (found out the first one was fine) tested the TBS. Tests fine. Tested wires to and from the APP, TBS, to and from the PCU. All giving me 5v. So why do I still have the SES & REP lights and no gas? Any help would be awesome. Thanks in Advance
2002 GMC Envoy 4.2L 4x4
Codes: P1275; P1635; P0453; P0113
(The last 2 seem to only come up after running for a short time. The first 2 come up right away after resetting the ECU)
 

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Hi again, please see my answer to your question in the other thread.

Just as an FYI, the key hint here is the P1635 Code which is saying there is a problem with the 5VDC reference circuit. I'm fairly sure the other 3 codes are a result of the problem with the 5VDC reference circuit.

Good Luck!
 

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Discussion Starter #3
Hi again, please see my answer to your question in the other thread.

Just as an FYI, the key hint here is the P1635 Code which is saying there is a problem with the 5VDC reference circuit. I'm fairly sure the other 3 codes are a result of the problem with the 5VDC reference circuit.

Good Luck!
Thank you! I'll start checking that tomorrow. I'm fairly flustered atm. I wish I had seen this msg earlier! I thought maybe it was the new fuel pump (cause the gas peddle worked b4 I put the new one in) so, for the 3rd time since I started this, I dropped the tank. This time removing the new pump and putting the old one back in. Now instead of P1275 & P1635 I get P1275 & P1280. I reset the computer after the swap and only ran it for a min. So the 5v code may still pop back up. But the new fuel pump, I had to literally SHOVE in and hold it down with my knee to get the ring back on and hold it down. Plus, it doesn't look EXACTLY like the old one. It came with a harness that acts like a converter. Making my oem harness a fit for it. I think it's a generic to fit multiple cars, but is it normal to have it so hard to fit down in the tank like that? And now that I'm getting a different code, should I still be looking at what you said b4? And should I go put the new tank back in again, or buy a new one that fits better? Ugh! This is so much fun... 🤦‍♀️ Thanks again for the help, I really do appreciate it.
 

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OK, so this is how I think you should proceed (or it's at least how I would proceed). First, unplug the electrical connector that goes to the electronic fan clutch and look over the wires that go towards the drivers side of the vehicle and rule out any worn insulation that could ground out the wires going between the PCM and the fan clutch.

Second, start the Envoy and if you have a code reader/scanner, plug it in and clear the codes. Now, does the engine run any better without the electronic fan clutch plugged in? If yes, they you know you have to replace the electronic fan clutch. If you need to replace your fan clutch please purchase one of the following brands: Hayden, Four Seasons (likely a relabeled Hayden), Behr (Mahle/Clevite), or ACDelco (likely a relabeled Behr). Yes, they are a little more expensive than some of the no-name generic fan clutches out there, but they are miles ahead in quality and reliability.

After replacing the fan clutch (provided that it was the problem), scan for OBDII codes again and clear any OBDII codes. Now start driving normally.

OK, now moving onto your fuel pump assembly, I know exactly what you mean about having to use your knees to press it down far enough so you can get the lock ring installed using your hands. Also, it pays to be a midget and to have an extra 3 or 4 arms in order to do this task in under 38 seconds!:eek:

I just replaced the fuel pump in our 1999 Buick Century a short while ago, and the new pump I got was much springier than the one it replaced (and both were Delphi pumps). There was a small oblong shaped access opening in the trunk so I got to lie on my belly with the trunk latch sticking me in the gut right below the belly button in order to replace the pump.

OK, the P1275 code is for the one side of the accelerator pedal position sensor, and the P1280 code is for the other side of the accelerator pedal position sensor. It's a redundant system to make sure all is well. Since both sides are throwing a code, I really think it has to do with a bad fan clutch or something in the 5 VDC reference circuit.

New pumps might look a little different from the older pumps, but not so much as to question if it's the correct pump or not. Also, for all the TrailBlazer/Envoy fuel pumps I have seen, they come with an electrical pigtail installed on them for attaching to the wiring harness.

Try and find out where the new fuel pump came from and what brand it is. Most of us on here will only use ACDelco or Delphi fuel pumps because we do not want to have to do the job again especially if the fuel tank has to be dropped. On one of the other GM forums I frequent, one guy purchased a new fuel pump from Rockauto for something like $50.00 to put into his son's truck. Well, that $50 fuel pump did not even last 2 weeks before it died. He had the trucked towed back to his house and he threw in a new Delphi or ACDelco pump.

Please keep us advised, and we're more than willing to assist. There are several very knowledgeable members (some of whom do this for a living) on this forum, so if one of us gets stuck, we can draw on the knowledge and expertise of one or more of the other members.

Take care and good luck!
 

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Discussion Starter #5
Thank you! I will be working on this first thing in the morning. I was starting to feel pretty lonely out here in "electronic idiot acre". When I first looked at the throttle I was like "where the f is the cable??" I have zero experience in the electronic part of vehicles. So I'm super glad I found you. And I had never done a fuel pump b4 so, your input on that makes me feel much better. I'll go ahead and put the new one back in, since it would be more trouble than it's worth to send back. I was thinking about getting one of those wire probe units to track down the 5v issue as well.
But I'll start with the inspection of the fan clutch, and let u know how it goes! Super grateful for all your help. Ttys
 

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You are quite welcome! Yes, electronic throttle bodies are allegedly the latest and greatest things, until something malfunctions.

One of the best "electronic testing tools" to get would be a Digital Multi-Meter (DMM). Relatively inexpensive, yet very flexible. A DMM can be used to test for voltage, current, resistance, etc. One I really like, is the Innova 3320, which sells for about $30 online at Amazon & Walmart.com. It does all the basic things and is not overly complicated.
 

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Regarding the fuel pump, it's very likely a Chinese knock off of a knock off based on the prices I see on their e-bay store. Just as an FYI, their Better Business Bureau rating is F, and from the complaints I read, they sell junky fuel pumps with lifetime warranties but they do not stand behind the warranty when the fuel pump dies.

Cut your losses early and put in a Delphi or an ACDelco fuel pump. If you are driving a standard wheelbase Envoy, and not the EXT version (longer one) the ACDelco part number is MU1837 and it sells for $170.79 at RockAuto, and the Delphi unit's part number is FG0387, and it sells for $197.79 (Amazon.com prices are about the same).
 

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Discussion Starter #9 (Edited)
Oh I have a DMM. I just only recently learned and am learning how to use it. I was referring to the wire probe kits that help you track down broken wires without actually probing the wire. I seen cheap ones for like $30+ on Amazon.
Oh, that's nice.. (about the fuel pumps) ok, well as the saying goes, u get what you pay for.. trite but true. I guess I'll order that while I sort out the gas pedal issue.
 

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OK on already owning a DMM and learning how to use it! I have zero experience with broken wire detectors other than my eyeballs.

Yes, I know it sucks big time, but better to find out now, than sometime down the road when you are on a trip, or in a hurry to get to an important appointment and then have it die.

A couple of other things from our collective bag of tricks/experiences: ACDelco 41-103 Iridium spark plugs are the preferred spark plugs according to feedback from the 4.2 L I6 engines. These engines are extremely picky about what plugs go into them and if they do not get their 41-103 plugs, they will throw misfire codes and have driveability problems. For Oxygen sensors, use only Denso or ACDelco O2 sensors unless you want to have problems. For other engine management components, stick with ACDelco, Delphi, or Standard Motor Products/BWD parts. Now most brands of parts have at least two tiers of parts - a premium level and a value level, and some have a mid-level tier. Stick with the mid-level to premium level parts as they are generally manufactured with better quality materials and under more rigorous quality controls. Most of us also will advise to stay away from Dorman sensors and electronic components unless you absolutely positively cannot find the part from one of the other manufacturers.

OK, that's it from me for tonight. I think I've saddled you with enough information!
 
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Oh yes, one other thing (actually 2). If you do not have a Haynes manual for your Envoy, I strongly recommend getting one. It is worth it's weight in the most precious metal in the universe. Also, here is a link to an online Chilton's manual that is aimed at the more experienced DIY-ers: Chilton Auto Repair

Good Luck!
 

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Discussion Starter #12
Thank you. I’m up am working at it now. So far I’ve unhooked the fan, started it up and getting the same. I just cleared the codes and am resetting the ecu to see if that helps. And just to be sure, the fan clutch has only the one harness on top to the drivers side right?
 

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Discussion Starter #13 (Edited)
First, unplug the electrical connector that goes to the electronic fan clutch and look over the wires that go towards the drivers side of the vehicle and rule out any worn insulation that could ground out the wires going between the PCM and the fan clutch.
So I unhooked this and nothing changed. Looking over the wires now, so far they all look fine. If there was a problem in the wiring for the fan clutch, and that was indeed the problem, should the gas pedal be working with the clutch unplugged? And since it's not, does that rule that out as being the problem? I bought a wire probe kit today. So I'll be able to follow the wires to figure out if there's a break. I'll start with the fan clutch wires, but where else should I go from there?

Regarding the fuel pump. So far I've left in the old one, since it didn't seem to make a difference in the current problem. I'll worry about that after I get the gas pedal working again. Since it was working before I changed the pump to begin with. And putting the old one back in didn't seem to change anything, I'm assuming the pump had nothing to do with this part.
 

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OK, so the fan clutch is not the problem, and yes, there is only one connection to . Check and make sure the wires going to the throttle body are all intact and that the connector going into the throttle body is seated properly. Within the last week or so, another member described similar symptoms, and it turned out to be a bad wire in the harness going to the throttle body. Also, unplug that connector and look at the terminals and make sure they are clean. While you have the wire harness disconnected, this would also be a good time to remove the throttle body and clean it. But, read this first:


That way you do not strip the internal gears in the throttle body.

Also, there is a ground wire inside the passenger compartment of the TrailBlazer that can cause trouble for the accelerator pedal sensors. It is located on the driver's side of the transmission hump just about inline with where your foot rests on the gas pedal. Sometimes the area corrodes, sometimes the bolt gets loose. Just clean up the metal and the ring terminal and tighten the bolt back down.

Trying to rule things before you need to spend more money on parts.

Regarding your question about if the accelerator pedal position sensors would work with the fan clutch unplugged, the answer is yes.

Good Luck!
 

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Thank you! I will be working on this first thing in the morning. I was starting to feel pretty lonely out here in "electronic idiot acre". When I first looked at the throttle I was like "where the f is the cable??" I have zero experience in the electronic part of vehicles. So I'm super glad I found you. And I had never done a fuel pump b4 so, your input on that makes me feel much better. I'll go ahead and put the new one back in, since it would be more trouble than it's worth to send back. I was thinking about getting one of those wire probe units to track down the 5v issue as well.
But I'll start with the inspection of the fan clutch, and let u know how it goes! Super grateful for all your help. Ttys
I just put a fan clutch in my 04 eEnvoy I got a AC Delco from Rock auto cheaper than the aftermarket. Please did not go with a no name brand I put 2 of those in and within a year had to change them, I finally went OE and haven’t had a problem
 

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Discussion Starter #16 (Edited)
there is a ground wire inside the passenger compartment of the TrailBlazer that can cause trouble for the accelerator pedal sensors.
I'm trying to find this, not having much luck. Is it under the carpet? So I'd have to pull up the carpet to find it? However, what I do see, looks fine. On that note, the other day, trying to get to the pedal in the first place when I changed the APP sensor, I moved the seat back (they're electric seats) then, trying to get to and see all the wiring a couple days later, I took parts of the dash off.( Not all of it, just enough so I could pull the stereo out if I needed to.) And now there's a couple things:
One, I turned on the heater to see if / how well it works, and it sounds like there's an elephant sitting on it and I'm not sure the fan is moving.
Two, suddenly the seats don't work on either side. There's 3 fuses that I, so far, have found for them. In the fuse box under the back seat, all 3 are fine. I plugged everything in the dash back in thinking they were connected to something in there, (the 4x4 switch or the rear windshield wiper) still no power to the seats... What did I do that caused that..? and I'm still not having any luck with the gas pedal. Ugh!

I've unplugged the battery to reset the codes and still am only getting the 2 for the APP sensors 1 & 2. So I'm not sure why the 5v reference one doesn't every come up anymore.
And lastly, I've retested the TPS and the APP sensors and I'm getting 5v on all the wires I'm supposed to in those, but I read today that it's only supposed to get 4.87 at the most on those. Is that right?

Edit: I think I figured out the seat thing. While checking fuses yesterday I think when I checked the big fuse for the seats, when I put the fuse back in, it pushed one side of the connecting piece down in to the fuse box so one side of the fuse is just loose in the box. I tried to unbolt the box to get to the underneath and it's like a 3 layer fuse box and I can't get to the part that's loose... Nice. 🙄😕
 

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Discussion Starter #17
Oh, also I noticed when I just let it idle, the fuel pump relay gets really warm.. is that normal?
 

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Regarding post #17, strange. Sorry, yeas, it is under the carpet. Apologies for forgetting to mention that originally.

Regarding post #18, I do not think it should get that warm.

Time to call in the big guys. I'll send them an email and ask them to join in. Your patience is requested.

Message sent
 

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Discussion Starter #19
Ok, I'll check under the carpet for the ground and will otherwise be patient.
But I'm curious about the voltage thing. I read somewhere today that if it's over 4.87v it trips the REP, hence no gas pedal. So if that is in fact the case, how do I get the voltage down? And why is it up?
And the fuel pump relay doesn't get hot. Just pretty warm comparatively.
 

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Hmmm... Not sure about the voltage going over the 4.87 value. Only thing I can think of is that the 4.87 VDC is the maximum output voltage from the accelerator pedal sensors that go to the throttle body and control the throttle body. The 5 VDC reference voltage is fixed and there is no way to get that down.

Let's wait and see what the pros (Ravalli Surfer and TJBaker) have to say about this. I know one of them (Ravalli Surfer) has a lot of experience with the accelerator pedal position sensors/assembly.
 
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