GM 4.2L Six Cylinder Engine Sensor Locations

Typical engine data sensor and control component locations on the GM 4.2 L engine.
Click sensor description below image for sensor details.

Please consider making a small Tip/Donation.
1. PCM
2. Electronic throttle control
3. MAP Sensor
4. Throttle Body under air inlet
5. Fuel pressure regulator (FPR)
6. Intake Air Temp Sensor
7. Exhaust Cam Actuator Solenoid
8. Secondary Air Injection (AIR) Diverter valve
9. Exhaust Camshaft Position sensor
• 4.2L Serpentine Belt Routing Diagram

Question: where is the cam position sensor.
 Answer: 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.

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.

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

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.

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.

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.

I have an Oldsmobile 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.

Hi, 2004 GMC 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.

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.

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.

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.
 I Don't see anywhere in these comments anyone saying that there is not a coolant temperature sensor.

Have a 03 GMC Envoy were can the knock sensor be located?
 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.

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.

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.

My 2002 trailblazer died while driving. Will not turn over keeps blowing a PCM fuse.
 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.

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.