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Discussion Starter · #1 ·
I drive a 2003 Trailblazer LT. I love the truck, it's a heck of a machine but it is falling apart on me. About three days ago when I started my TB the fan sounded really loud. When I put it in gear and accelerated the fan was speeding up and getting louder. Not gonna lie it sounds pretty cool like a semi truck accelerating from a stop or something. I replaced the fan clutch about two years ago with some off brand clutch.

I'm getting the codes P1481 (cooling fan speed sensor) P0493 (fan overspeed) relating to this issue.

I have been busy and watching my temp gauge and oil pressure to make sure nothing serious happens and I keep driving but I had to get to work so I drove it. Yesterday when I was accelerating up to 70 mph, my TB lost power for a second and the "reduced engine power" light came on. I stopped at a gas station and when I started it up again the light was not in anymore. I was driving the TB today and the check engine light which has been on for the last three years started blinking and I got a P0300 (random/multiple cylinder misfire). I changed ask if the coils and spark plugs with Aldeco's about two years ago as well.

I have also been getting the following codes for months: P1345 (crankshaft/camshaft position), P0440 (Evaporative Emissions System), P0172 (system too rich bank 1), P0137 (o2 sensor circuit low voltage bank 1 sensor 2).

I believe there is something wrong with my electrical system of anyone has any insight. When I start the TB the "change engine oil" light comes on for about 10 seconds and then turns off. The cruise control does not work when I start up the TB cold but after driving it for about five minutes, if I shut off the engine and take the key out then start it back up my cruise will work. As of about 6 months ago my high beams do not work. If I try to flip the lever to turn them on my low beams go out and I have no headlights. Once I flip the high beam lever back my low beams work again. I have tried messaging with the relays because I have seen a lot of info on doing this when the low beams are having this issue but I could not find any info on anyone having this issue with the high beams. I also am having trouble with my turn signals and brake lights on any trailer I plug into the outlet on the back of my TB. This issue just started about the same time my high beam issue started. The running lights work on the trailers but the turn signals and brake lights will not register.

I apologize for the laundry list of issues and yes I realize I am a bad father to my TB but I figured what better place to ask then here. I have referenced this site for a very long time and it always has helped me fix my truck. Not sure if anyone will read through this all but it's worth a shot!
 

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I drive a 2003 Trailblazer LT. I love the truck, it's a heck of a machine but it is falling apart on me. About three days ago when I started my TB the fan sounded really loud. When I put it in gear and accelerated the fan was speeding up and getting louder. Not gonna lie it sounds pretty cool like a semi truck accelerating from a stop or something. I replaced the fan clutch about two years ago with some off brand clutch.

I'm getting the codes P1481 (cooling fan speed sensor) P0493 (fan overspeed) relating to this issue.

57120



The high speed fan is the result of the missing fan speed sensor issue.

The fan speed sensor uses the same 5 Volt DC power supply that the throttle and accelerator pedal sensors use. As such if there is an issue with the wiring of the fan speed sensor it can affect the signals from the throttle and or accelerator pedal sensors and that will trigger the reduced power mode that you experienced.
 

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Discussion Starter · #3 ·
View attachment 57120


The high speed fan is the result of the missing fan speed sensor issue.

The fan speed sensor uses the same 5 Volt DC power supply that the throttle and accelerator pedal sensors use. As such if there is an issue with the wiring of the fan speed sensor it can affect the signals from the throttle and or accelerator pedal sensors and that will trigger the reduced power mode that you experienced.
TJ, is this something that will require me to buy a new fan clutch, fuse or something else entirely? I'm not great at understanding the electrical side of cars but I like to fix everything else if I can.
 

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is this something that will require me to buy a new fan clutch, fuse or something else entirely
My advice/motto: Never buy or replace anything before proving it is required.

If you are willing we can guide you through the diagnostics.

A DMM (digital multi meter) is required.

An OBD2 adapter and smartphone app (less expensive ~$20) or a decent scantool that can read live data (more expensive but not neccesarily better) is also needed.
 

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Yes, you will have to replace the fan clutch. Get an AC/Delco fan clutch, unless you want to be doing this again in a couple of years. As TJ mentioned, the fan clutch shares a 5V reference signal with the throttle position sensor and the accelerator position sensor. That signal acting up will put the engine into limp mode until the key is cycled, which is why it started up normally after your gas station stop.
The oil light is indicating it's time for an oil change. If you've recently changed the oil, the light needs reset. Turn the key to on, but do not start the truck. Push the accelerator pedal down firmly, but not quickly, 3 times within 5 seconds. Turn the key to off. Start the truck and the light should be off.
It also sounds like your multi-function switch has gone funky on you. That switch controls high and low beams, turn signals, cruise control, wipers. Most of the stuff you've been having issues with. The truck is 18 years old and showing it's age. These things happen.
 

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Yes, you will have to replace the fan clutch.
At this moment this is entirely unproven. There is a hypothesis, an educated guess of sorts that is a possility. But it is unproven. It might fix this issue, or it might cost you a few hours work and a hundred something dollars and fix nothing. The choice of course is yours.
 

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TJBaker is correct. Diagnose first, repair second. You might find all you have is a broken wire.
 
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Discussion Starter · #8 ·
My advice/motto: Never buy or replace anything before proving it is required.

If you are willing we can guide you through the diagnostics.

A DMM (digital multi meter) is required.

An OBD2 adapter and smartphone app (less expensive ~$20) or a decent scantool that can read live data (more expensive but not neccesarily better) is also needed.

TJ,

I have a FOXWELL NT301 OBD2 Scanner that reads live data as well. That's how I got all of my codes. I have no idea what the live data means or how to interpret it though.

Thank you
 

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Discussion Starter · #10 ·
Yes, you will have to replace the fan clutch. Get an AC/Delco fan clutch, unless you want to be doing this again in a couple of years. As TJ mentioned, the fan clutch shares a 5V reference signal with the throttle position sensor and the accelerator position sensor. That signal acting up will put the engine into limp mode until the key is cycled, which is why it started up normally after your gas station stop.
The oil light is indicating it's time for an oil change. If you've recently changed the oil, the light needs reset. Turn the key to on, but do not start the truck. Push the accelerator pedal down firmly, but not quickly, 3 times within 5 seconds. Turn the key to off. Start the truck and the light should be off.
It also sounds like your multi-function switch has gone funky on you. That switch controls high and low beams, turn signals, cruise control, wipers. Most of the stuff you've been having issues with. The truck is 18 years old and showing it's age. These things happen.
Yes, you will have to replace the fan clutch. Get an AC/Delco fan clutch, unless you want to be doing this again in a couple of years. As TJ mentioned, the fan clutch shares a 5V reference signal with the throttle position sensor and the accelerator position sensor. That signal acting up will put the engine into limp mode until the key is cycled, which is why it started up normally after your gas station stop.
The oil light is indicating it's time for an oil change. If you've recently changed the oil, the light needs reset. Turn the key to on, but do not start the truck. Push the accelerator pedal down firmly, but not quickly, 3 times within 5 seconds. Turn the key to off. Start the truck and the light should be off.
It also sounds like your multi-function switch has gone funky on you. That switch controls high and low beams, turn signals, cruise control, wipers. Most of the stuff you've been having issues with. The truck is 18 years old and showing it's age. These things happen.
Flyboy,

I appreciate the help! I will probably be buying that new multi-function switch asap. I really appreciate the insight into the change oil light. I just changed it but it doesn't care. I'm going to try that reset you mentioned. I'm going to check to make sure there are no broken wires but will definitely get the Acdelco brand fan clutch if I have to replace mine.
 

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Discussion Starter · #12 ·
Among the live data parameters, look for a cooling fan speed value .

Do you have a multimeter for testing voltages and resistances?
TJ,

Yeah I have a multimeter. Alright I'm going to look for the fan speed value on the live data tomorrow. Am I using the multimeter to touch to the cooling fan wires then?
 

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Am I using the multimeter to touch to the cooling fan wires then?

One quick edit here... before doing any multimeter testing I would look for that fan speed signal in the luve data of the scantool first.

There are a few tests that can be done fairly easily. First off a brief description of the 2 circuits involved in the fan clutch.

There is a speed sensor with 3 wires and a solenoid valve with 2 wires.

The speed sensor is called a hall effect sensor and is frequently used to sense the speed of rotating objects. It is powered by a 5 volt DC power source within the PCM so there is a 5 volt positive wire and a low reference (ground) wire. A third wire is used for the pulse that tells the PCM the fan speed. There are 6 pulses per revolution of the fan.

The fan clutch solenoid circuit is fed by the fan relay control module. It sends Pulse Width Modulated power as directed by the PCM. You may see some people saying you can test this solenoid function by jumping a 12 volt power source directly to the solenoid. I will say right here DO NOT DO THIS! In my experience this will immediately short out the solenoid circuitry as it was never designed for this.

So what to test? The P1481 code indicates the PCM is not getting a fan speed signal. It could be a loss of power to the sensor or more likely a wiring fault. To start out I usually check for 5 volt power, low reference (ground), and a signal output at the connector on the fan shroud. Using a probe set or a very thin needle allows for testing the circuit in situ. Here I am testing the 5 volt power to the speed sensor....

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It's definitely the fan clutch. I have an 04. These vehicles are POS..I Got All kinds of issues with mine too. They're lemons.
 

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Discussion Starter · #15 ·
It's definitely the fan clutch. I have an 04. These vehicles are POS..I Got All kinds of issues with mine too. They're lemons.
Rob,

Yeah mine has been having all kinds of weird issues. Today the "service 4wd" light came on randomly. The 4wd hadn't worked in years since around the time I changed my front wheel hubs but the switch to put it into 2HI, A4WD, 4 HI and 4LO has always lit up and blinked in between changing it and I could hear a mechanical noise trying to activate it. When the "service 4wd" light came on the switch to put it into 2HI, A4WD, 4 HI and 4LO light was not on at all and there was no noise. I got to work and the next time I started it the "service 4wd" light wasn't on and my 4wd switch light was back on.

I just replaced the fan clutch about two years ago along with the water pump and serpentine belt. I'm going to take TJ's advice first and see if I can rule out all options before I buy a new one. I've just been super busy and driving the spare. I love my TB but dang it is getting old.

I appreciate the feedback. I will probably buy the Acdelco fan clutch off Amazon and return it if I find out it is something else before it gets here.
 

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Discussion Starter · #16 ·
One quick edit here... before doing any multimeter testing I would look for that fan speed signal in the luve data of the scantool first.

There are a few tests that can be done fairly easily. First off a brief description of the 2 circuits involved in the fan clutch.

There is a speed sensor with 3 wires and a solenoid valve with 2 wires.

The speed sensor is called a hall effect sensor and is frequently used to sense the speed of rotating objects. It is powered by a 5 volt DC power source within the PCM so there is a 5 volt positive wire and a low reference (ground) wire. A third wire is used for the pulse that tells the PCM the fan speed. There are 6 pulses per revolution of the fan.

The fan clutch solenoid circuit is fed by the fan relay control module. It sends Pulse Width Modulated power as directed by the PCM. You may see some people saying you can test this solenoid function by jumping a 12 volt power source directly to the solenoid. I will say right here DO NOT DO THIS! In my experience this will immediately short out the solenoid circuitry as it was never designed for this.

So what to test? The P1481 code indicates the PCM is not getting a fan speed signal. It could be a loss of power to the sensor or more likely a wiring fault. To start out I usually check for 5 volt power, low reference (ground), and a signal output at the connector on the fan shroud. Using a probe set or a very thin needle allows for testing the circuit in situ. Here I am testing the 5 volt power to the speed sensor....

View attachment 57128
TJ,

I'm going to get under the hood tomorrow hopefully if it isn't pouring and test it out. I really appreciate the feedback and advice. This site has always been great to me even though I have never posted before.
 

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Coming to this discussion late. There is an easy way to tell if a clutch is bad. At startup the fan will be engaged then should spin freely shortly afterwards. I have used a rag and stick to rub against rim of fan ring. If good, it should be disengaged and able to come to a friction stop. If it is shaking while stopped thats an indication fan bearings are bad. If it cannot be freely stopped and is frozen then it is a not a good one.
 

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It's definitely the fan clutch. I have an 04. These vehicles are POS..I Got All kinds of issues with mine too. They're lemons.
Not exactly accurate, or helpful. I have an '03 Envoy and don't have near the problems. Sounds to me like an "I'll get to it when I have more time/money." maintenance routine, that's catching up with him.
 

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Coming to this discussion late. There is an easy way to tell if a clutch is bad. At startup the fan will be engaged then should spin freely shortly afterwards
Not entirely accurate. It can take two minutes at greater than 2000 rpm to disengage a fan clutch so trying to stop a fan that has not been disengaged in this way is risky at best and tells you nada.

Anyone having fan clutch issues should begin by reading this post linked below to learn just what they are dealing with...

 

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With the fan issue, check the wiring at the fan connector. I had an issue several years ago and decided to replace the clutch fan. As soon as I completed the job, started it up and had the same error. WTF..~! Just dumb luck something caught my eye and I saw a broken wire at that connector. Fixed it and put RTV silicone over the wires to help with the bouncing so they do not break again. No codes.
How old is your battery..? These "new" vehicles are so dependent on the battery being good that is it's low or have a bad cell, funky electrical issue will/can arise.
 
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