Top 10 2004 GMC Envoy Questions & Answers

I have a 2005 Envoy with a 4.2..... Just recently the check engine light illuminated so I read the code after replacing the 20amp fuse labeled cigar. My OBDII connection had no power so if you plug your reader in and nothing check the fuse under the hood labeled "cigar"
After pulling the code P0410 Secondary Air Injection Malfunction I checked the operation of the air pump by removing the hose connected to the solenoid. By the way the solenoid is located on the pass side of the engine top towards the back. After pulling the hose off the solenoid I started the vehicle when it was cold and after 20 seconds or so the pump should turn on and blow air out of the hose. Once I verified the pump was operating I pulled the solenoid then placing jumpers from the Positive & Negative of the battery to the pins on the solenoid. You should be able to hear the solenoid click which says its operating. But mine did nothing so I read across the pins with an Ohm meter and verified the coil was good.
So take some good penetrating oil and fill the inside of the valve with it. You can see the plunger shaft assy in the opening and thats the area you want to fill with a good penetrating oil!!!! Let it sit for a couple of hours keeping it full of oil. The housing is aluminum and the shaft is likely to be a brass material so rust is not possible. Its caused by a buildup of carbon!! The penetrating oil will soften the carbon which in turn will free up the plunger!! MINE WORKS GREAT NOW and plus you will save around $140.00 if you were to buy it from the dealer!!! Or $80.00 aftermarket from RockAuto.com

With out doubt it is the Indicator Flash Unit (Found near fuses) its a plug type box. you pull it out, plug in new one and it works. (Kinda looks like a strange adaptor plug you would put in a power socket.

I am having the same problem. Here is my part.
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I cannot locate the part that I have removed from my vehicle anywhere on the web. I only find that other part. I called the dealer with the info posted here. I gave them the last 8 of my vin# and he said they had the part AND the adapter for $110.84. I'm heading to the dealer to pick it up now.

The thermostat on this vehicle's (the Envoy & Trailblazer are essentially the same vehicle) In-line 6 cylinder engine is on the driver's side of the engine, below & behind the alternator. It is not found in the typical location (which may be for the 8 cylinder engine), in an answer above.

Most directions outline removal of the alternator to gain easy access to the hose clamps, bolts and housing of the thermostat. I have located a site that after free registration, has detailed instructions on how to do this job, and the link below that describes an easier method with photos. Check out:

http://forums.trailvoy.com/showthread.php?t=54225&highlight=replace+thermostat

its in the fuse panel under the hood there should be a chart on the cover

Do you live in a dusty area? My sister lives in dusty New Mexico and had a malfunctioning XUV tailgate. My reasoning was that something must tell the tailgate not to drop down if the glass is up, and if it can't tell, then it will only open sideways.
So we removed the trim panel, and the tailgate was indeed full of dust. By reaching my arm in, I found two plastic optical sensors which tell the gate whether the glass is up or down; both were coated with dust. After cleaning these the tailgate was back to its normal operation. The two sensors are flat, round - about the size of a nickel or dime...I couldn't see them, just found them by guessing that they must be there. Hope this helps!

P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

What does that mean?
This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125

In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.

Symptoms:
You will likely not notice any drivability problems other than the MIL illumination.

Causes:
A code P0128 may mean that one or more of the following has happened:
* Low engine coolant level
* Leaking or stuck open thermostat
* Faulty cooling fan (running too much)
* Faulty coolant temperature (ECT) sensor
* Faulty intake air temperature (IAT) sensor

Possible Solutions:
Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:
* Verify coolant strength & level
* Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
* Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
* Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
* If the above items check out good, replace the thermostat
* If Nissan vehicle, check for a TSB such as this one. The ECM may need to be reprogrammed to correct the P0128 code

Hope helps (remember rated and commet this).

There is a technical service bulletin regarding this problem with 2004 GMC envoy. Actually there are 3 separate issues with regards to the elecronic tailgate. The reason why the dealers are backordered is the part you want keeps failing after a time of being installed.

For the particular problem you have of the electronic latch not working, the bulletin recommends a inspection of the endgate connector C900. Look for the wires to be backed out of the connector or not properly crimped. To crimp you will need a crimping tool available at any electrical supply shop. The connectors can be had from the dealers.

The other solution referred to intermittent operation of the endgate but can apply in your situation also. For that, look for chaffing at the wire harness connectors for the endgate actuators located at the upper right and lower left latches. They have been found to be pinched up to 8 inches away from the actuators. In this situation it would be ideal to replace the connectors and install in a way so wires will not be pinched.

The other thing to look out for is dusty sensors. For this you will need to remove the tailgate trim panel and locate the 2 optical sensors on either side. You can feel them with your hand, they will be the size of a nickel. Clean all the dust under the trim. In addition to that you should open the switch and use contact cleaner to clean out any dust or debris inside there. There is no mechanical way to open the door once the electronic side has malfunctioned without damaging the door. I hope this helps.

The number 3 plug is the third one back from the front of the engine. They are numbered in order 1,2,3,4,5,6 front to back, this is the cylinder numbers not the firing order. Firing order is 1-5-3-6-2-4 .

Below are some diagrams for you. If you have the XL model there it will be different for the rear passenger compartment fuse panel which I did not include. I did include if you had a 6 or 8 cylinder engine for the under the hood fuse panel because there is a difference. This should be in your owners manual if you have one. If you do not and would like a copy, you can email me at [email protected] with your make, model and year and I will be happy to email you a copy. I hope this helps and good luck.