GM 4.2l 4200 inline 6 cylinder engine data sensor locations and picture.
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1. Powertrain Control Module (PCM)         2. Electronic throttle control           3. MAP sensor
Typical engine data sensor and control component locations on the GM 4.2 L engine.
Click on number for a description.
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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.
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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.
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.
More Comments>>>
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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.

GM 4.2L Six Cylinder Engine Sensor Locations



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