Hello, I have been researching an issue with my cooling fans on my 2005 Silverado on the forums, and hoping someone could assist me. With my scanner hooked to the truck, the engine temperature will go up to 220F and fans will not come on. After reading several forums on the issue, I understand that there are two wires that are "grounded" in the PCM to make the fans cut on. They are a GN wire in Connector 1, Pin 42 AND a Blue wire Connector 2, Pin 33 of the PCM. If I ground either of these wires (at the PCM) the fans will cut on and operate. This tells me that the circuit is fine from the PCM, through fuses & relays, out to the fan. Correct? It seems like my PCM is bad. OR is it possible that a ground to the PCM is bad? Parameters in the PCM? ANY HELP WILL BE GREAT. I have troubleshot the system all the way to these two PCM wires, and grounding them is the only way to get the fans to run..... Thanks (There are NO fan related codes in the PCM by the way....).
2005 Silverado Z71 cooling fans not working.
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Grit03
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I have the same year, make and model and this has helped me eliminate a lot of possibilities when mine started doing the same thing. Did you ever end up having to replace the PCM?
Thanks again, this thread saved me a lot of time!
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Hi guys I am having similar issue with my 2011 fans won’t come on even if I turn on the ac . I have replaced the relay and temp control sensor for them . I’ve bypassed the relay and they spin fine .
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Bumping this thread. My '07 Classic is having the exact same issue right now. No fans, A/C doesn't work, no fans when A/C is selected on the control panel. I've replaced all fan relays, fuses checked fine, replaced coolant temp sensor. Fans turn on if I jump the relay slots 30 to 87. I've even swapped ECUs and still no change.
2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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Alternately/as well, you can try doing electrical testing instead of throwing parts at the truck. Could be a wiring or connector problem somewhere, or perhaps the hvac head unit has a problem.
if the refrigerant lever is low, it will not come in either. You could just short out the refrigerant pressure switch and see if it comes on or alternatively disconnect the coolant temperature sensor.
That's what happened to mine
twice
That's what happened to mine
twice
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Hello everyone I have had a problem also with my Electric fans not turning on when at temp mine was the relay on the fans but I also switch to a manual fan and clutch to stop the over heating
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What year/make/model/engine/trim truck?
Hi,did you ever resolved this problem?i got 59 chevy with 2004 Silverado 1500 4.8 engine swap with same problem,i could only remember fans coming on once since i bought it last year when it was ticking over, checked fuses,fan does work when hot wired, temp sensor works on obd scanner,it boiled up yesterday and can't find the issue, thanks tom
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I've been chasing my tail on this same problem (2005 GMC Sierra 5.3, Z71, Auto-Air, etc...
What I'm about to copy/paste here is my notes as I diagnosed this system... sorry if it's a little cryptic.
I've watched videos and some are exceptionally good and useful if you want to understand the Series/Parallel system - fascinating! ( a good video here )
OK --- There are a lot of things that have to be in perfect planetary alignment to make it all work well. Beware that some of the circuits that qualify the fans and HVAC operation are both digital (CANBUS) and analog (Class 2 Com) --- etc., so be sure you know where you are poking that probe tip!
I start with the fuses --- and I found some interesting things that don't make any sense at all --- but I'll post my latest adventure.
Here's my first chapter --- enjoy.
////// * \\\\\\
Look in center panel and go to: Battery Supply 1 of 2
Look at the three relays --- two have a 40A fuse and the one in the center has a 10A fuse.
I'm interested in the center 10Amp fused relay. I cannot follow to where and from what the two connexs go-come-arrive ... all I see is the energizing circuit, not what the points energize or ground.
Here's the symptoms ---
The compressor and fans are inoperative for any/all HVAC settings.
The scanner says the command is coming from the HVAC Control Head >>> OK.
There is no Apply Voltage to the compressor clutch
The fans APPEAR to have 3-speeds --- but maybe only 2. This is not confirmed yet.
The engine, when it hits 205°F - then the fans both go on High Speed and eventually cycle off as the CTS is satisfied.
The cluster gauge works WNL.
The scanner reports the same values as the dash gauge says it is.
I assume this is the only CTS for both the computer and the gauge. (this is correct)
![Image]()
Jumping the Low Pressure sensor on the Reciever-drier does not do anything.
I cannot find any voltage going to the clutch, but there is a digital signal from the 3-point connex that I BELIEVE reports the pressure in the freon lines.
At rest, there is @160lbs pressure in the High Side; this is enough to qualify the system I believe. (I later found this is too high!)
If the #3/10Amp relay is removed, the fans don't operate even if the CTS says it needs them to run.
Plugging the #3/10Amp relay in when the command from the CTS is ON --- the fans (plural) go into High Speed.
I have confirmed that #1/40Amp relay runs the right cooling fan ... and ... the #2/40Amp relay runs the left cooling fan ...
.......... these results were established by jumping the #30 lug to #87 on the circuit board for each relay --- and the individual fans worked. <yippee>
![Image]()
#3 /10Amp relay (picture posted above ^) ) is a 5-pin version and to understand the 4-pin types, ignore the pin #87a--- so it is a simple two way On-Off circuit --- and with this I agree --- but WHAT doe it turn On/Off? (I didn't know at this point --- but it was a-coming!)
(continued on the next blank page because I sdomn't know if I've exceeded the image file size limit.)
What I'm about to copy/paste here is my notes as I diagnosed this system... sorry if it's a little cryptic.
I've watched videos and some are exceptionally good and useful if you want to understand the Series/Parallel system - fascinating! ( a good video here )
OK --- There are a lot of things that have to be in perfect planetary alignment to make it all work well. Beware that some of the circuits that qualify the fans and HVAC operation are both digital (CANBUS) and analog (Class 2 Com) --- etc., so be sure you know where you are poking that probe tip!
I start with the fuses --- and I found some interesting things that don't make any sense at all --- but I'll post my latest adventure.
Here's my first chapter --- enjoy.
////// * \\\\\\
Look in center panel and go to: Battery Supply 1 of 2
Look at the three relays --- two have a 40A fuse and the one in the center has a 10A fuse.
I'm interested in the center 10Amp fused relay. I cannot follow to where and from what the two connexs go-come-arrive ... all I see is the energizing circuit, not what the points energize or ground.
Here's the symptoms ---
The compressor and fans are inoperative for any/all HVAC settings.
The scanner says the command is coming from the HVAC Control Head >>> OK.
There is no Apply Voltage to the compressor clutch
The fans APPEAR to have 3-speeds --- but maybe only 2. This is not confirmed yet.
The engine, when it hits 205°F - then the fans both go on High Speed and eventually cycle off as the CTS is satisfied.
The cluster gauge works WNL.
The scanner reports the same values as the dash gauge says it is.
I assume this is the only CTS for both the computer and the gauge. (this is correct)
Jumping the Low Pressure sensor on the Reciever-drier does not do anything.
I cannot find any voltage going to the clutch, but there is a digital signal from the 3-point connex that I BELIEVE reports the pressure in the freon lines.
At rest, there is @160lbs pressure in the High Side; this is enough to qualify the system I believe. (I later found this is too high!)
If the #3/10Amp relay is removed, the fans don't operate even if the CTS says it needs them to run.
Plugging the #3/10Amp relay in when the command from the CTS is ON --- the fans (plural) go into High Speed.
I have confirmed that #1/40Amp relay runs the right cooling fan ... and ... the #2/40Amp relay runs the left cooling fan ...
.......... these results were established by jumping the #30 lug to #87 on the circuit board for each relay --- and the individual fans worked. <yippee>
#3 /10Amp relay (picture posted above ^) ) is a 5-pin version and to understand the 4-pin types, ignore the pin #87a--- so it is a simple two way On-Off circuit --- and with this I agree --- but WHAT doe it turn On/Off? (I didn't know at this point --- but it was a-coming!)
(continued on the next blank page because I sdomn't know if I've exceeded the image file size limit.)
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OK --- this si going to be l-o-n-g I know --- but if you want to know what I've found out so far ---- ok?
///// * \\\\\
I found where the rest of the cooling fan relays go to (provided it is a Manual system).
This is great information --- but I think it's for the Manual HVAC system .... I dunnow.
![Image]()
I see what is going on. The left cooling fan gets grounded through Relay 3 to complete it's circuit and turn on.
The cooling fan sequence is something like left fan and right fan both come on slow speed. Then one fan comes on at high speed and then both fans come on at high speed.
In reading the diagnostic procedure for "Cooling Fan Always On" it appears that the 5 pin relay (Relay 3) is the "control relay" and the 4 pin relays are the slow speed and high speed relays.
I'm attaching the Cooling Fan Always On diagnostic chart.
This is a PDF and it will need to download into some place of your choice ... FILE HERE
This is very confusing....
When I jump the individual fan relays (#s 1, 2) the fans individually come on High, not together; that is to say that the Relays #1 & #2 are drivers for one fan each, at High Speed.
If I take out R3, both of the high Speed cooling fans turn off even when the engine is over 205°F.
The power to these relays changes --- I THINK that pins # 85 & 86 then are at 12V, possibly from circuit feedback that doesn't mean anything to the circuit as it's supposed to be in High Speed and this just adds harmless redundancy to the circuit.
I've gotta go out after breakfast and re-check my results.
Amazon shows 2 CTSs --- (A/C DELCO # 213-4333 is one) - but they say there's only ONE SENSOR --- what gives?!@?
PS ---> I did find that R#2 drives the Left Fan and R#1 drives the Right Fan .... both at high speed --- but this may be the sign of a problem in the BCM or HVAC module
At this point, it looks like R#2 & R#3 - besides being for the individual fans (left & right) only produces High Speed, each.I think I just said that ... sorry.
I have yet to find anything that produces Low speed or the combination of one fan on Low and the other on High to produce a pseudo-Medium Speed.
Addenda:
My "sources" say there are two GM part numbers and 2 ACDelco part numbers for the same Engine Coolant Temperature sensor. GM Part Numbers are 12608814 and 19236568, and the ACDelco Part Numbers are 213-4333 and 213-4514,
Now, all 4 of these part numbers cross to SMP Part Number TX89. Confused? Yup --- I am.
(continued on the next white page )
///// * \\\\\
I found where the rest of the cooling fan relays go to (provided it is a Manual system).
This is great information --- but I think it's for the Manual HVAC system .... I dunnow.
I see what is going on. The left cooling fan gets grounded through Relay 3 to complete it's circuit and turn on.
The cooling fan sequence is something like left fan and right fan both come on slow speed. Then one fan comes on at high speed and then both fans come on at high speed.
In reading the diagnostic procedure for "Cooling Fan Always On" it appears that the 5 pin relay (Relay 3) is the "control relay" and the 4 pin relays are the slow speed and high speed relays.
I'm attaching the Cooling Fan Always On diagnostic chart.
This is a PDF and it will need to download into some place of your choice ... FILE HERE
This is very confusing....
When I jump the individual fan relays (#s 1, 2) the fans individually come on High, not together; that is to say that the Relays #1 & #2 are drivers for one fan each, at High Speed.
If I take out R3, both of the high Speed cooling fans turn off even when the engine is over 205°F.
The power to these relays changes --- I THINK that pins # 85 & 86 then are at 12V, possibly from circuit feedback that doesn't mean anything to the circuit as it's supposed to be in High Speed and this just adds harmless redundancy to the circuit.
I've gotta go out after breakfast and re-check my results.
Amazon shows 2 CTSs --- (A/C DELCO # 213-4333 is one) - but they say there's only ONE SENSOR --- what gives?!@?
PS ---> I did find that R#2 drives the Left Fan and R#1 drives the Right Fan .... both at high speed --- but this may be the sign of a problem in the BCM or HVAC module
At this point, it looks like R#2 & R#3 - besides being for the individual fans (left & right) only produces High Speed, each.I think I just said that ... sorry.
I have yet to find anything that produces Low speed or the combination of one fan on Low and the other on High to produce a pseudo-Medium Speed.
Addenda:
My "sources" say there are two GM part numbers and 2 ACDelco part numbers for the same Engine Coolant Temperature sensor. GM Part Numbers are 12608814 and 19236568, and the ACDelco Part Numbers are 213-4333 and 213-4514,
Now, all 4 of these part numbers cross to SMP Part Number TX89. Confused? Yup --- I am.
(continued on the next white page )
Unfortunately its little bit harder for me as most of the truck is custom made, wiring is bit ****ed up,got relay plug marked up cooling fan without relay but i have never removed nothing and nobody has touched my truck since i owned it,i have no ac either..
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There's a lot more of this kinda information from this point on ---
............. here's the link to get the whole document for yourself ---> LINK HERE - is a PDF. FIXED - I HOPE
I know this may not apply to your situation 100% --- but I don't think this has been collated into a few posts yet on any site ... just trying to be helpful here ... OK?
(on to the next page )
2004 Sierra 3500 6.0L, auto, extended cab, cab&chassis, upgraded to 4wd
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...url towards end of post #34 isn't valid, looks like it's mostly a url to a file on the poster's computer...
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Lemme see what I screwed up ...
Can you activate
Sorry did you say you can activate the fan with your scanner?if yes what diag scanner is it?i got cheap shite obd scanner but no function to activate components and older delphi but no Silverado on there :/
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