How a cigarette lighter fuse can cause you to pull your hair out

My mom drives a 1999 Lumina, doesn't have a lot of money (doesn't get much from social security each month and has no retirement), and when she has a car problem, she comes to me. Well, she wanted her oil changed last weekend, and she mentioned that her car would overheat if it sat still too long, but it's fine as long as she's driving. I told her it must be the cooling fans not coming on, she told me not to worry about it because she knew how to handle it (she would turn the car off when at a stop light or in a drive thru). She was also complaining that her AC needed to be charged. I told her that it wouldn't get as cold if the cooling fans weren't working either, so I'd look into it while I was changing her oil.

So my cousin and I started with the usual suspects; Fuses and relays for the fans. Fuses all checked out, tested all the relays... everything looked good. So, out comes the multimeter and we start checking all the wiring. We can't find anything wrong with the wiring, all the hot wires are hot, we checked continuity between the PCM (Powertrain Control Module, basically the car's computer) and the relays, etc, all clear. Unplug the coolant temperature sensor, and the fans don't come on, turn on the AC, they don't come on. So, it's looking like the PCM is faulty. I replaced it with one from ebay. Still nothing.

My cousin then wants to see if there's any codes with his OBD2 scan tool (there's no check engine light) but it comes up with some kind of error, and he asks if the cigarette lighter fuse is blown because according to him that can cause issues with the scan tool sometimes (I had never heard that but ok...) I told him I think she had said the cigarette lighter didn't work before because she couldn't get a charger to work. I checked the fuse... sure enough, it was blown. I replace the fuse with an extra from my truck and as soon as I plug it in and he turns the switch for his scan tool, the fans come on.

This info wasn't anywhere on the internet. Everything we read said check the fan fuses/relays, replace the PCM, check grounds, check continuity of the wires... nobody ever mentioned that the cigarette lighter fuse could be a problem. Why that would be an issue... I have no clue. It doesn't make sense at all for that to have any bearing on whether or not the cooling fans will work, but I wish I had known before I replaced the PCM.

So, for anyone out there who has an older GM car and the cooling fans aren't working and you can't figure out why... check your cigarette lighter fuse.

a reply to: Aldakoopa

Right on dude. Ive been driving a car for 4 years without the fans coming on. Also the cigarette lighter doesnt work. You gave me an idea. Either way im going to keep driving ol reliable

a reply to: Aldakoopa

I had a car back in the 90's that had a similar issue. Fans would not work if the in-line fuse to the radio was blown.

You said in the beginning you checked all of the fuses?? Am I missing something? I'm a auto electronics specialist for a living. First thing is always fuses and then grounds.

a reply to: Aldakoopa

On a lot of models of vehicles the manufacturers, in their infinite wisdom, put the OBD2 power on the Data Link Connector on the same circuit as the cigarette lighter, or power point. Then other things like O2 sensor heaters, voltage to the coolant sensor for the fans, etc. That is why originally you could not scan for codes. There was no power to the DLC.

For instance a common Honda problem is a check engine light for an O2 sensor failure that the local parts counter failure person will scan for you for free and sell you a $150 O2 sensor to fix the issue.

The actual issue most times is that the heater for the O2 sensor is on the same circuit as the cigarette lighter, which the owner blew doing who knows what but if the O2 heater doesn't work it sets a rather immediate code.

A good mechanic will normally take this into consideration when troubleshooting an electrical issue, particularly if it is a powertrain management problem

originally posted by: infolurker
a reply to: Aldakoopa

I had a car back in the 90's that had a similar issue. Fans would not work if the in-line fuse to the radio was blown.

Did it happen to be a GM car?

originally posted by: WUNK22
You said in the beginning you checked all of the fuses?? Am I missing something? I'm a auto electronics specialist for a living. First thing is always fuses and then grounds.

I only checked fuses related to the fans. I would have never thought in a million years that the cigarette lighter fuse would have anything to do with it. I edited my post to clarify a bit, hopefully.

PS: I'm a body man/painter, not really a mechanic. I have enough knowledge to get me by but I'm mostly a google mechanic to be honest, especially when it comes to electrical issues.

originally posted by: Aldakoopa

originally posted by: infolurker
a reply to: Aldakoopa

I had a car back in the 90's that had a similar issue. Fans would not work if the in-line fuse to the radio was blown.

Did it happen to be a GM car?

Geo / Chevy Spectrum. I think it was an Isuzu Imark with a chevy emblem on it.

originally posted by: infolurker

originally posted by: Aldakoopa

originally posted by: infolurker
a reply to: Aldakoopa

I had a car back in the 90's that had a similar issue. Fans would not work if the in-line fuse to the radio was blown.

Did it happen to be a GM car?

Geo / Chevy Spectrum. I think it was an Isuzu Imark with a chevy emblem on it.

Close enough.

originally posted by: GreyScale
a reply to: Aldakoopa

On a lot of models of vehicles the manufacturers, in their infinite wisdom, put the OBD2 power on the Data Link Connector on the same circuit as the cigarette lighter, or power point. Then other things like O2 sensor heaters, voltage to the coolant sensor for the fans, etc. That is why originally you could not scan for codes. There was no power to the DLC.

For instance a common Honda problem is a check engine light for an O2 sensor failure that the local parts counter failure person will scan for you for free and sell you a $150 O2 sensor to fix the issue.

The actual issue most times is that the heater for the O2 sensor is on the same circuit as the cigarette lighter, which the owner blew doing who knows what but if the O2 heater doesn't work it sets a rather immediate code.

A good mechanic will normally take this into consideration when troubleshooting an electrical issue, particularly if it is a powertrain management problem

That's good to know. Now I know to start checking absolutely all the fuses when I'm having an issue even if I think they're unrelated.

Save yourself a bunch of headaches and buy a testlight power probe. Instead of just telling you if have power or a short, it can also push 12v through the probe. It's a huge time saver, you can check relays, solenoids, etc...

Also nice if your working alone. It's hard to have your head in the engine bay listening for a relay when your the guy who has to turn the key or press buttons.

a reply to: Aldakoopa

If you are right there at the fuse block, you've got a test light in your hand and something is wrong, it doesn't take too much of your time to just test everything that is hot at key on.

Cars nowadays are so interconnected that it isn't funny.

I had a car that, sometimes, the cruise control didn't work. No codes, no indicators, no anything. The cruise control would shut off while driving and then you could reset it and it would work for a month. Or two minutes.

It drove me a little crazy for awhile but eventually I found the problem. It was the coolant temperature sensor.

The connection to it was bad, so sometimes, if you hit a bump just the right way, it would disconnect, for just an instant. When it did that, the PCM would see the circuit as an open. An open, or infinite resistance to the PCM, meant that the coolant temperature was seen as 40 below zero. The programming for the PCM did not allow cruise control to work if the coolant temperature was below freezing.

So I replaced the connector on the sensor to fix the cruise control.

It has to be hard to not be a mechanic and track things down nowadays. We have resources like dealer sites and alldata and others.

If you run into another problem, feel free to PM me. Master mechanic since 1994.

originally posted by: Natas0114
Save yourself a bunch of headaches and buy a testlight power probe. Instead of just telling you if have power or a short, it can also push 12v through the probe. It's a huge time saver, you can check relays, solenoids, etc...

My multimeter and a jumper wire told me everything I could possibly know in this case. The cigarette lighter evidently had something to do with the PCM that caused it not to run the fans. Does sound like the power probe could have saved me some time though.

a reply to: Aldakoopa

It sounds like they were wired in series. Why anyone would wire the car's cigarette lighter in series with an AC fan is beyond me though.

here`s a little tip for cooling fan problems, if you turn the A/C on the cooling fans will run constantly because the A/C condenser needs a lot of constant air flow so the A/C circuit bypasses all the normal temperature controls and sensors that control the cooling fans and keeps the fans running constantly.
so, if your temp gauge goes up higher than normal just turn your A/C on for a few minutes and the gauge will go back to normal.

in a related story of weird car things, a few years ago a bought an old 1983 chevy pickup and it started having problems with the dash lights, they would only work if the high beams were on.
after doing the normal things like replacing the light switch and the high beam actuator switch,replacing the printed circuit film on the back of the gauges,checking for loose and broken grounds etc i still had the problem.

i was about to give up on trying to fix it so as a last resort i checked the fuse, even though i was sure it couldn`t be the fuse because the dash lights worked when the high beams were on, well it was the fuse.

after further checking i found that the high beam indicator bulb is on a different circuit and fuse than the rest of the gauge lights and that even though the gauge light fuse was burned out the gauge lights were getting power through the high beam indicator light circuit. when the high beams were turned on and the high beam indicator light on the dash came on it feed power to all the other gauge lights.

so, anyhow i relearned a valuable lesson whenever you have electrical problems with your vehicle the first thing to do is to check ALL the fuses because car makers seem to do some pretty unusual things with their electrical stuff.

originally posted by: GreyScale
a reply to: Aldakoopa

If you are right there at the fuse block, you've got a test light in your hand and something is wrong, it doesn't take too much of your time to just test everything that is hot at key on.

The problem was all the fan fuses and relays were under the hood. The cigarette lighter fuse was inside the car in the side of the dashboard. I checked all the fuses and relays that were under the hood while I was there, but didn't bother with the ones inside the car because, at the time, I thought they were irrelevant.

If you run into another problem, feel free to PM me. Master mechanic since 1994.

I'll keep that in mind. Thanks.

originally posted by: Tardacus
here`s a little tip for cooling fan problems, if you turn the A/C on the cooling fans will run constantly because the A/C condenser needs a lot of constant air flow so the A/C circuit bypasses all the normal temperature controls and sensors that control the cooling fans and keeps the fans running constantly.
so, if your temp gauge goes up higher than normal just turn your A/C on for a few minutes and the gauge will go back to normal.

The fans wouldn't work at all, unless I used a jumper wire to ground the relays like the PCM is supposed to do. Turning the AC on wouldn't turn the fans on because that, too, was controlled by the PCM and was affected by the cigarette lighter fuse, for whatever reason. I even unplugged the coolant temperature sensor which, in theory, should read as infinite resistance to the PCM and at least in the case of the car I was working on, read as a very high temperature and the PCM should kick the fans on high, but it wouldn't do it until I replaced the 15 amp cigarette lighter fuse.

originally posted by: Natas0114
Save yourself a bunch of headaches and buy a testlight power probe. Instead of just telling you if have power or a short, it can also push 12v through the probe. It's a huge time saver, you can check relays, solenoids, etc...

Also nice if your working alone. It's hard to have your head in the engine bay listening for a relay when your the guy who has to turn the key or press buttons.

Ive been using the power probes sense they came out. Just got the 3s last week. Probably one of the best tools out there for electrical work. Very nice to have a 12v power source at your finger tips and being able to check for a good ground is also very helpful.

a reply to: Aldakoopa

You said all the hot wires were hot.....

If the wiring to the fan goes hot the fan will turn on or the fan motor is bad.

I don't see why you would change the PCM. If the fan wire is going hot then the PCM is doing its job. If your fan wire is hot but the fan doesn't turn on then your fan motor is bad not the PCM.

a reply to: Aldakoopa

I hooked my engine fan up to be manually turn on and off,after installing an electric fan on my truck,I am not impressed with management system in new cars,million wires,when used to be one