1. Powertrain Control Module (PCM) 2. Electronic throttle control 3. MAP sensor
4. Throttle Body under air inlet 5. Fuel pressure regulator 6. Intake Air Temp Sensor (IAT)
| Typical engine data sensor and control component locations on the GM 4.2 L engine. Click on number for a description. |
7. Exhaust Cam Actuator Solenoid
8. Secondary Air Injection (AIR) Diverter valve
| 12-19-10 where is the cam position sensor. |
Comments
| From the front of the truck, it is located on the passenger side front of the engine. Just below the valve cover. Number 9 above. |
9
9. Exhaust Camshaft Position sensor
| 12-21-10 04 GMC envoy 4.2L can you tell me where is can find coolant below temperature sensor. |
| There is no such sensor. I am guessing that you have a check engine light with code P0128- coolant temp below thermostat regulating temperature. This code is cause by either low coolant level, or more likely- a bad thermostat. |
| 1-7-11 where is the throttle body |
| The electronic throttle body, or TAC is located at position 2 in the picture above. The large air intake runner with the word Vortec to the left needs to be removed to get to. |
| 3-12-11 WHERE ARE THE SPARK PLUGS AND THE PLUG WIRES |
| This engine does not actually have spark plug wires. They are spark plug boots. They are located under the ignition coils on top of the engine. The spark plugs are down in the valve cover under each coil under the air box on top of the engine. |
| 3-13-11 THANK YOU FOR THE ANSWER. DO THESE SPARK PLUG BOOTS HAVE TO BE REPLACED AND HOW OFTEN, AND WHAT KIND OF SPARK PLUGS WOULD YOU RECOMMEND FOR THIS ENGINE. |
| The boots are part of the coils. They do not need to be replaced for maintenance. I would recommend AC Delco spark plugs. |
| 3-13-11 getting trouble code for secondary air injection. Replaced valve and pump, light stayed off for 120 miles but came back on so then replaced primary oxygen sensor. Light went out for a day or two but then came back on with same code,secondary air injection. |
| You say you replaced the valve. Which valve. There are 2 diverter valves and 1 vacuum control valve / solenoid. O2 sensor would not cause AIR code. |
| 4-11-11 I'm HAVING A HESITATION WHEN YOU FIRST GIVE IT GAS , WHAT COULD THAT BE. |
| Most commonly, that problem is due to a dirty or excessive amounts of carbon inside the throttle body. A good cleaning will resolve most issues. You can check on this website to find out the proper cleaning procedure if you don't know how. Check your air filter too and replace if dirty. |
| 4-13-11 HOW DO YOU CHANGE THE EXHAUST CAMSHAFT POSITION SENSOR AS I'm GETTING A CODE FOR IT IN MY 03 TRAILBLAZER. |
| 6-17-11 Where is 1997278 evap valve located on 2002 trailblazer? |
| I think that part number is for the EVAP vent valve, and it is located underneath the vehicle, back by the gas tank, attached to a hose that leads to the EVAP canister. It is easiest to replace by getting the Trailblazer up in the air, either on a lift or on jack stands. There is one electrical connector on it, and one hose connection. It is usually retained to the bracket by a small, bendable metal tab that you can bend out to remove it and then bend it back in after the new one is on. For future reference, the other valve/solenoid for the EVAP system is the Purge Solenoid, and it is located up by the intake manifold. |
| 6-21-11 I have a 1999 Chevy Tahoe 5.7 and have a sensor wire without a home....it is a ROUND plug near thermostat housing and a DRK GRN /wht and a lt grn wire....cant figure out what sensor it goes to ???? ANY HELP WOULD BE GREATLY APPRECIATED !!!!! |
| 6-21-11 If the check engine light is not on, then it may just be an unused connector. Sometimes there are extra connectors depending on engine size, options, ETC. Look inside the electrical terminals. If they are rusted or dirty, then that means they were never plugged into anything in the first place. |
| 7-22-11 I have '02 Bravada/idles very rough especially when A/C or heater is on/or stopped with vehicle in gear/all started when I disconnected battery to try to reset auto load level compressor/may have been coincidence/but idled and ran great until then |
| You may have a carbon buildup in the throttle. After a battery disconnect, then computer tries to reset the idle. If the is a lot of carbon, it cannot find a stable idle. A good cleaning may just be needed. |
| 8-2-11 i have a 2004 GMC envoy with a 4200 in-line 6 cylinder. It has rough idling and some times it stalls. How do i clean the throttle body and what part needs to be cleaned ? Or is that something else. |
| See link in last post above labeled "Carbon Buildup In The Throttle" for cleaning procedure. |
| 8-6-11 When i turn on the motor without the AC on it idles just fine ,but when i turn the AC on it turns off or the ac won't come on for a 2004 trailblazer LS with the 4.2 litre motor. |
| 8-18-11 your website is great! Thank you for the information! |
| Thank you ! Come visit us again ! |
| 9-20-11 Hi,2004 envoy 4x4 SUV,the service 4WD light came on this morning and hasn't since. Any thoughts? This a Canadian truck. |
| Would need to know the code it set, but you could be looking at a 4WD switch problem, encoder motor, or possibly a transfer case control module. Any of these would need some diagnosing by an experienced technician. You could have an intermittent problem, since the light is off now, and could be ok for the time being. |
| 9-22-11 2003 Trailblazer EXT....the rear fan AC works intermittently...I can't find any bad switches so what could be causing this?? |
| It could be the rear blower motor itself, or a bad blower resistor which is bolted to the rear HVAC case. |
| 10-11-11 where is the o2 sensor located - thats the code getting from meter. |
| 11-2-11 I have a 4.2 ;when I put it in to drive it has a slight shake but when i put it in reverse it does not. After it warms up for about 10 to 15 min it goes away. |
| 11-8-11 A slight vibration? Well, that could be a bad engine mount, since the engine torques to the left in drive, and the opposite direction when in reverse. |
| 11-13-11 Rough Idle even after cleaning the throttle body. The idle is ok when the engine is cold, but worsens as the rpm drops as the engine warms. |
| You may have a problem with the valve in the cylinder head. Have seen several times a rough idle causing a slight misfire on one or more cylinders caused by the valves and valve seats not sealing. |
| 11-13-11 Thermostat for 2004 trailblazer is not the same the store says it should be. Is it the same one as Gmc stat? Or the change I heard about? Where the stat is separate from housing? |
| 11-14-11 Where is temperature coolant sensor located. |
| 11-14-11 Where is crank position sensor located. |
| The crank sensor is located on the drivers side of the engine block as seen either though the wheel well or from under the truck. |
| 11-25-11 i've located the MAP Sensor....how do i release the clips to replace it. |
| 11-25-11 Pinch the little tabs carefully and pry up on sensor with a small screwdriver. Be careful, they break easily. |
| 12-14-11 If what you are saying is true and that the Vortec inline 6 has no coolant temperature sensor then why does auto zone sell one ?Duralast/Coolant Temperature Sensor for your 2004 GMC Truck Envoy 4WD 4.2L SFI DOHC 6cyl. Price: $29.99 Please help me before i spend money. |
| Don't see anywhere in these comments anyone saying that there is not a coolant temperature sensor. |
| 12-25-11 Where is the engine temperature sensor located on a GM 4.2 liter engine? |
| 12-31-11 I think the coolant temperature sensor is located on the left side of the engine. You can see it through the wheel well opening. |
| 1-2-12 Have a 03 GMC Envoy were can the knock sensor be located? |
| 1-11-12 Where is the oil sending unit located on the 04 Trailblazer 4.2L 6cyl? I have been told several things, on top of the block and down beside the oil filter. Which is correct? |
| That depends on which engine you have in your GMC Envoy. On the V8, they are located under the intake manifold. On the 4.1L straight 6 cylinder, they are on the drivers side of the block just above the oil pan. One near the front of the engine, one near the back. |
| The oil pressure sender is located on the oil filter housing. |
| 1-20-12 Where are the oxygen sensors located on the 2003 GMC Sierra 4.8 v8 4wd 1/2 ton pickup. |
| 1-21-12 2004 GMC Envoy XUV idle very hard at around 500 rpm then feels like engine is shaking under hood feels like it is trying to get exhaust out or something. Exhaust coming out very white smoke. |
| 1-23-12 Olds Bravada..Where is the camshaft position sensor located?Please help |
| Sounds like it is running very rich, like a stuck open fuel injector. |
| 2-5-12 My 2002 envoy service engine light comes on plus reduce power like comes on also and shuts off. |
| 2-6-12 I have the same issue...2002 envoy service engine light comes on then reduced power...npow my battery is drained and nothing...wont start or take a charge,,,maybe battery too dead for system? |
| Common is that the throttle is full of carbon and needs to be cleaned out. |
| 2-15-12 Were is secondary air injection system? |
| The A.I.R. system is comprised of several different components. The pump and relay are under the drivers side frame rail. The pipes come up the back of the motor. The diverter valve is on the passenger side of the cylinder head. Number 8 in the picture above. |
| 3-4-12 For those who want a pcv vale on their 2003 4.2 Disconnect hose from no. 2(ETC) insert an air tight connector connect a 3/8 I.D. hose route it around no. 3 and connect back to no. 2 nipple. Go on opposite side 0f no. 3 and splice in a Fram no. 12 filter (a gas filter) it will filter or clean up returning vapor to air in take. Point the filter in proper direction. |
| 3-4-12 Have a 2004 Trailblazer inline6 Vortec (engine service light comes on )#3 Misfire then goes out for a few days, then comes back on. Where is the sensor located that controls this. Replaced plugs and boots and moved coil, still pops on and off #3 Misfire. Have not leak checked or compression checked yet. Also, I have seen the daylight sensor flash red in the past but not for a while.(little dome/bulb in center of dash by windshield. Is this tied to the security system? My car alarm only works when I open the back hatch but it used to work when any door was attempted to be opened after set. How can I reset the alarm so any door handle pulled will set of the alarm. What the monkeys is going on with this thing. |
| As for the misfire, I'd recommend a compression test and/or leakdown test. Doubtful it's a bad injector, and since you've changed/moved the ignition components, the only thing left is a mechanical problem. Those heads have a history of misfire problems, you'll probably be looking at cylinder head replacement to fix your problem. Also, the ambient light sensor does not flash at all. If you've got an aftermarket alarm installed you'll have to see the installer to fix any problems. |
| 3-18-12 What is the location of the EGR Valve 2005 Trail Blazer 4.2 L. |
| This engine does not have an EGR Valve. |
| 3-20-12 My shop keeps telling me my Vortec Solenoid is leaking oil and it's getting on the fan belt. Looking myself I do see a sensor looking device with an electrical connection. This device is where you have the Exhaust Cam Actuator Solenoid labeled in your photo. This device is oily and does appear to be leaking. Is this the Vortec solenoid my shop is referring to? It looks easy to change, is it? Thank you. |
| Ok, first of all, there is no sensor on your vehicle called a vortec solenoid. Whoever is telling you this does not know what they are talking about. I'm sure what they are referring to is the cam actuator solenoid that you see yourself is leaking oil. That is the normal thing to leak on the Trailblazers and cause problems. Replace it and you should be fine |
| 3-24-12 There was a question asked on this page that wasn't answered that I'm having a problem with. I have a 2004 Envoy that when u turn the AC on it drags the motor down and wants 2 stall out. Checked freon level and has plenty. What could be causing this issue? I also have a code that Autozone is telling me on their scanner is Fan Speed Sensor but it doesn't show up in their system. Does anyone know where that sensor is located and is it a dealer part only? A fix for these problems would be greatly appreciated. Thx. |
| Your GMC could have either a throttle full of carbon or the compressor is locking up. Clean the throttle body first and then re-evaluate. Fan speed is usually a bad fan clutch assembly. |
| 4-2-12 What is the function of the vent valve on 2003 envoy 4.2 |
| See this link for an explanation of the EVAP Vent Valve. |
| 4-7-12 What are symptoms of a bad oil pressure sending unit. This is a 2004 GMC Envoy 4WD. And where is it located? Please help :) |
| 4-7-12 2003 Bravada is getting P0440 Evap Crtl System Malfunction. Have replaced gas cap/no help. Where is the canister, common fails/fixes? |
| 4-7-12 My 2002 trailblazer died while driving. Will not turn over keeps blowing a PCM fuse. |
| A fluctuating gauge is a common problem of a bad pressure sender. On the straight 6 it is located by the oil filter, on the housing, |
| You are going to have to start moving around harnesses to find the shorted wire. Check on the left side frame rail near the A.I.R. pump. |
| I have a 2003 Trailblazer with the 4.2 Vortec inline 6 cylinder and it makes a what I call a pinging sound when I throttle up at slow speeds. This ping/rattle doesn't persist after the speed has been reached and only re-occurs after I slow and give it the gas. I am burning only regular gasoline at 87 octane. I do not use the gasolines that have the alcohol additives if I can find gas without it. Earlier this year I had a problem with the engine idle speed which was a dirty throttle body and after I cleaned it runs perfectly. I found this recommendation in the post above and used carburetor cleaner to remove the carbon deposits that had collected where the baffle comes to rest on idle. |
| It depends where the noise is coming from. If you are sure it form under the hood, take a look at the belt and pulleys. |
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| For more information on the confusion of this comment see the bottom of this page P0128. |
| Howdy, scenario: I have a 2003 GMC Envoy SLT with the 6 cylinder and approx 190k miles. It has been getting terrible gas mileage, erratic idle and stumbled during free revs. When I had the codes checked it suggested that I replace the coolant temperature sensor as well as the intake temperature sensor. I changed both sensors over the past weekend and now the stumble off idle is gone and idles like a kitten, but the gas mileage is still not the best and now when I turn the fan switch on, the motor stumbles to the point of dying during idle, if turned on while at driving speed there is a significant lag in power and extremely noticible drop in gas mileage. Question: by chance even though the battery was disconnected for over an hour, do I still need to reset the computer or possibly clear the codes out or something to get this car running correctly? |
| There is no reset of the computer that will fix a problem. At best it will erase the stored codes until a fault occurs. The intake temperature sensor can effect fuel economy, as well as the coolant temp sensor. Have the computer scanned to see if either code came back. Check the throttle for carbon buildup for the idle problem, check for a leaking 5.7L Vortec fuel pressure regulator. |
| Looking for the seat belt warning chime fuse this is not working at all, also rear defogger works sometimes got power to the connectors , also look like someone had a sign inside the rear window , had this truck for two months, check the rear defogger grind couldn't find a break. |
| There is no fuse for the seatbelts. You may have a bad belt. If there was a sign in the rear window, then there IS a break in the grid. |
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