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Discussion Starter · #1 ·
I have a 2008 Cadillac DTS that is running hot. There is an issue the with the cooling fan not working properly, I just replaced the complete fan assembly yesterday and the same issue persists. The fans do not run unless the AC is on, with the AC on only the passenger side fan runs, this happened with both the old fan assembly and the new one. I checked and tested the relays there good, I replaced them with new ones anyway, inline fuse looks good and tested good but I didn't replace that. I replaced the thermostat yesterday too for good measure. Coolant is good and is at the correct level in the tank, cap is good replaced the cap for good measure. Still the same problem persists the fan does not come on, I let the car idle with the AC on for 1hr until it the engine temp reached 230 (have a basic cheap OBD!! tester plugged in) the fans do not come on, let it sit for hours retried the same idle test with the AC on for 1 hr temp reaches 216 and then fluctuates between 210 and 220, however I cannot be out on the road with only one fan, I live in Florida where it is Hot AF all the time. I can't figure this out and it is driving me insane, I also tested the connectors that plug into each fan, the test good, so what is the problem? I don't get it, I probably didn't even have to replace the fan assembly but I did anyway. The only thing left I can think of is the engine temperature sensor which is located in an unreachable area on the lower back side of the engine by the firewall. Any help would be appreciated.
 

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2002 F55 STS, 2014 Explorer XLT, F-150s
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Welcome to Cadillac Forums.

With no A/C function set your cooling fans should go to SLOW at about 216 or so and FAST at about 225. With some A/C or DEFROST set they both should run at all times. Fans do not normally run at over about 30 mph - not needed. Fan operation was changed at the end of the 2005 model year, about June of 2005. The newer "DTS" that replaced the Devilles has a different fan sequence that earlier.

The thermostat is set to begin opening at 188 and fully open at 206. Most Northstars run at 190 - 210 all day every day except while at unreasonably long idle times or in heavy traffic with no A/C set.

Have the car scanned at a local parts store and post any codes and definitions found.

Yes, the ECT is a bitch to get to, but does the dash gauge work? If so, it's not the ECT.

3 relays, a couple of circuit fuses and two maxi-fuses. My 2002 schematic is different from yours, so subscribe the car to the online GM/Cadillac service manuals at www.alldatadiy.com. There's a DTC menu at the top of the main menu on the left side of the home page for your car.

Do you speak "purge line" ? If that's clogged you get oddball overheats, too. It runs from the hollow bolt/nipple at the water crossover to the upper side of the surge tank.
 

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'93 SedanDeville 60 Special
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Sounds like it could be the ECT sensor issue

What temps does the dash gauge report and what does ECT on OBD scanner report (compare)?
Can you see the coolant fan command PID in the scanner to see if the PCM is commanding the relay ?
Maybe a wiring problem from pin of PCM to relay ?
Have a OBD-II scanner that has bi-directional and you command fans on

Have you used a multi meter at where the PCM wire to relay is and see if commands coil of that relay ?
debugged for fan and relay grounds OK ?
 

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Discussion Starter · #4 ·
The dash temp gauge and the obdII reader I have seem to match, the dash does not tell in numbers just the old fashioned thermostat gauge.

The car has consistently produce lean codes for both banks P0171 and P0174. The issue here I have yet to discover.

Additionally this all started to happen two weeks ago when the car would not start. Starter needed replaced. After replacing the starter a week later the car would not start again, realized it was the park sensor popped off, starts fine now. When this happened the second time a multitude of codes came up, U0101 and U0100, not communicating with ecm and tcm, along with lean codes as usual P0171, P0174, and P0411 incorrect air flow along with the car running hot from the fan issue. Now after clearing the codes and running multiple times only the lean codes come on. Something happened the second time it would not start from the park sensor popping off. Still why is the driver side fan not coming on, and why does the fan not come on without the AC?
 

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P 0171 and P 0174 usually point to large vacuum leaks - on the later Northstars it's either the PCV piping or the rubber connector between the intake manifold and throttlebody. Prior to 2000 the big leak was the intake manifold overpressure valve.
 

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Discussion Starter · #6 ·
P 0171 and P 0174 usually point to large vacuum leaks - on the later Northstars it's either the PCV piping or the rubber connector between the intake manifold and throttlebody. Prior to 2000 the big leak was the intake manifold overpressure valve.
When I changed the starter I replaced the intake manifold gaskets and the I checked the rubber connector accordion gasket between the intake and throttebody looks like new so I didn't replace that one. Lean codes existed before and after this.
 

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Discussion Starter · #7 ·
When I changed the starter I replaced the intake manifold gaskets and the I checked the rubber connector accordion gasket between the intake and throttebody looks like new so I didn't replace that one. Lean codes existed before and after this.
However yes I think I'm going to replace both the piping and the gasket your referring too. But after I fix this problem with the cooling fan as its urgent.
 

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P 0411 refers to the secondary AIR system that supplies fresh air to the exhaust manifolds during cold starts in order to quickly light of the cat. Blower in the LF fenderwell front end, air piping, vacuum lines, solenoid, and controls on top of the right (rear) cam cover.

The AIR valve(s) can develop heavy carbon deposits on the check valve area and that screws up airflow, and so does/do cracked plastic vacuum control piping. Any of that small plastic piping and the rubber connecrtors can be replaced with lengths of rubber vacuum line from any parts store.
 

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Discussion Starter · #9 ·
Sounds like it could be the ECT sensor issue

What temps does the dash gauge report and what does ECT on OBD scanner report (compare)?
Can you see the coolant fan command PID in the scanner to see if the PCM is commanding the relay ?
Maybe a wiring problem from pin of PCM to relay ?
Have a OBD-II scanner that has bi-directional and you command fans on

Have you used a multi meter at where the PCM wire to relay is and see if commands coil of that relay ?
debugged for fan and relay grounds OK ?
I don't have a OBD-II scanner that can has bi-directional commands just a cheap $40 scanner, also cannot see the PID
to see if the PCM is commanding the relay. Trying to get a mechanic over here tomorrow with a scanner.

Used a Multimeter on the Relays but have yet to check the PCM wire to the relay.
Checked ground. Also disconnected the battery for a 24hr period to let it reset.
 

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Would be a lot easier if you could post the wiring schematic from PCM to fans and A/C wiring
I assume 2 fuses involved and checked ?
Feel good the relays swapped did not solve the problem ? as hints of wiring to multi relay issue ?

Using multi meter you should be able to tell if the PCM is turning relay coils by ground or B+ (12V)
and compare that circuit when no fans on to when fan is on if PCM and wire from it is OK

How does this work,
either one fan on for low and both fans on for high

Or both fans on either at a low or high rotation ?

Is this the type of relays used ?

594762
 

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Two 4-pin relays are used for fan ON/OFF and one 5-pin relay is used for speed - fans set to parallel (FAST) or series (SLOW) operation.

The 4-pin relays are internally wired diagonally and can be inserted two ways; the 5-pin goes in one way only.

No provision for one fan operation - both operate in either FAST or SLOW.
 

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Here is the PCM fan settings for that model and year with and without A/C on or off

594771
 

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Discussion Starter · #13 ·
I replaced Fuse Number 27 (J Type Fuse 30amps) and it works.
The old fuse looked fine through the viewing both although the plastic was old and brittle to the touch so I said alright just replace it and sure enough both fans powered up. Both fans should turn on without the A/C on when the Desired Fan Power Vs Coolant Temp reaches 213F or (101C) and they do. However what caused this fuse to blow out to begin with? I still don't know?

Also I think the factory 213F temperature is to high for this engine to reach for the fans to come on, is there a way to make these fans come on when the temp reaches 205F? A simple solution for me is to just run the A/C 24/7 not an issue as I live in Florida and put some coolant additive to keep the coolant temp down, and yes the additive does work In dex6, ran it for years. But I wish there was a way to make the fans turn on at 205 instead of 213 if seems way to high for this aluminum engine as it will easily reach 220/225 for a couple minutes before the fans start bringing it back down to the 200 mark.

Someone from another forum sent me the GM Manual page for this
This how the fans operate:
Quoted from the GM manual for the 2008 Cadillac DTS:
"During low speed operation, the ECM or PCM supplies the ground path for the low speed fan relay, which is fan 1 relay 33, through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closed the relay contacts, and supplies battery positive voltage from the fan 1 fuse 27 through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the series/parallel relay which is fan 3 relay 32, and the right cooling fan. The result is a series circuit with both fans running at low speed.

"During high speed operation, the ECM or PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3-second delay, the ECM or PCM supplies a ground path for the series/parallel relay and the high speed fan relay, which is fan 2 relay 31, through the high speed cooling fan relay control circuit. This energized closing the relay contacts, and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit, to the right cooling fan. During high speed fan operation both engine cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.

supplies battery positive voltage from the fan 1 fuse Number 27 through the cooling fan motor supply voltage circuit to the left cooling fan. The fuse looked fine as you can see through the viewing box so I did not think it could be this fuse but I put a new one in and both fans power up.

When the request for fan activation is withdrawn, the fan may not turn OFF until the ignition switch is moved to the OFF position or the vehicle speed exceeds approximately 10mph. This is to prevent a fan from cycling ON and OFF excessively at idle"

And I got a coffee afterwards in my Cadillac. Hence my username.
 

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Post #2 - fuse and relay paragraph.

The thermostat is not fully open until 206. The engines are designed to run at 190 - 210 degrees. 213 or 225 is nowhere NEAR even warm for the Northstar. The engine doesn't even go into Camel Mode until near 270 degrees. If it ain't broke, don't fix it.

No, the water wetter does NOT work - the thermostat regulates engine temperature. Coolant already contains water wetter - surfactants - and the system pressure is designed to efficiently move heat from the engine metal to the coolant. DO NOT fool with so-called "low temperature" thermostats unless you want a real Pandora's Box of trouble codes, rich mixtures, poor fuel mileage and performance loss.

You're over-thinking the so-called cooling problems. Let the engine run as designed.
 

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Like Submariner409 said the Northstar is designed to run at the temp set at the factory. Also lowering the temp would affect the transmission too. Modern cars have modules that talk to each other and making a change can be like a domino effect and cause unanticipated issues.
 
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