Not sure if this is the right place for this question - but figured it was a good of place if any.

My check engine light keeps flashing at me - too regular to be an intermittent short, but I do not get any codes. All I get when I try to read the codes is the code 12.

It doesn't flash all the time, it comes and goes randomly. It happens when I first thing in the morning when I drive to work (flashing periodically - meaning it will flash for about 10 seconds, goes unlit for a brief period of time, then starts flashing again. Sometimes it's 10 seconds, other times, it goes on for about 45 seconds)

Makes me almost wish for a code to be stored.

Any ideas?

The only mod that is on the car is that the previous owner had wired up one of the fans (I have an 88 Iroc Convertible with TPI and Auto with Dual Fans) so it runs all the time. The way he did it seems to be he disconected the plug that plugs into the radiator (I assume it was a plug as it appears he cut it off) and ran a wire along the passenger side fender back towards the distributor area.

I had thought about trying to undo his mod but before I try to dig into that wanted some suggestions. I have recently changed the plugs, wires, cap and rotor as well as the air filter. All the levels (i.e. oil and coolant) appear correct.

Could it be related to sensor/switch that is on the passenger side of the radiator that is no longer connected? Anyone know what it does?

 

The switch on the radiator is the "low coolant level alarm" sensor. I don't think your car has that, but the radiators all come equipped with it anyway (the same rad fits a bunch of cars that do have the alarm). It has nothing to do with the fan.

The fan switch is in the pass side head, between the #6 & #8 spark plugs. And of course, the ECM also has an input to the fan.

Hard to say what the PO pretended he was doing to the car.... sounds like a bunch of typical pointless wire hacking, as usual. Might be a good idea to follow the extra wire, see what it goes to, and get rid of it; and put the wiring back like it's supposed to be. That's where I'd start if it was mine.

 

The sensor that you refer to is actually a fan relay mounted there. See picture.

 

Trickster - thanks for posting the wiring harness drawing. It looks like I have all the relays that are in your drawing and they are all connected - although the one that is closest to the radiator in the front is no longer mounted (it's just laying in the battery tray) - I'll have to find some sheet metal screws to put it back up.

Here is a pic of the "disconnected" sensor on the radiator that I was refering to. You can also see where the start of the wire the prior owner had spliced into the black/red wire coming out of the passenger side fan.

Any ideas what the sensor is?

 

Here is a pic of where the wire ends by the distributor.

Any ideas? Think it would be safe just to remove the wire and tape up the splices? It looks like I have all of the relays still intact. Any ideas how to determine if they work without risking the car (overheating it)?

 

I almost didn't spot it in that picture. Is it sitting just slightly above the radiator hose there? There are two possible things that come to mind here, although I have to admit I have never to my knowledge seen either one before. They are 1. as RB83l69 mentioned, a LOW COOLANT LEVEL ALARM sensor or 2. a TRANSMISSION FLUID TEMPERTURE sensor. Will have to check on that. I have gone through my GM service manual, haynes, and chilton manuals. None of them make any mention of this being an option in the car. Something else I came across in a owners manual for a 86 firebird is an ENGINE COOLANT TEMPERTURE warning light. I can't say that sensor might not serve the same purpose as the sensor in the left side of the engine by the #1 spark plug.

 

The sensor looking thing in the radiator tank just above the lower rad hose nipple, with the single blade terminal, is definitely the "low coolant level" one. So there probably isn't a wire to go to it; it's just "surplus" from the rad being for multiple applications.

Looks like the PO connected from the distributor 12V feed wire (big pink wire) to the fan's 12V lead. So it's using ignition power to directly operate the fan motor. Very stupid, as it makes the switched ignition circuit provide all of the fan motor current whenever the factory circuitry isn't calling for the fan... very likely to burn up things like the wiring and ignition switch, as well as potentially reducing the voltage available to the distributor, and therefore making the ignition weaker.

I'd suggest doing away with that wire, and re-soldering the wires it hooks to so that they don't develp bad connections, and taping them up as tightly as possible. I don't think it's possible to get heat-shrink tubing onto either of them very easily.

 

Trickster - You are correct, the sensor is the thing with the single blade connector just above the radiator hose. Sorry for not making it clearer.

RB83L69 - If it's just a "low coolant" sensor, which the cars did not come with, does this mean I have the wrong radiator? If not, I assume it's fine just leaving it alone.

As far as the extra wire for the fan, I had thought about removing it, but was concerned about overheating. I would expect most people who "tweak" the wiring would actually have a reason (i.e. it was overheating or the fans were not coming on). Any ideas how to check the components/fan system without risking overheating the car?

Thanks for all your help so far!

 

The replacement radiators for these cars also fit a number of other GM cars. Some of those others have the indicator. So rather than make 2 different radiators, the rad companies make only one so that they lower their production and inventory costs, and you just don't hook up the sensor in cars that don't need it. It doesn't hurt anything by being there.

In any case, if the radiator fits and cools the engine, then it's the right radiator; catalog listings or whatever notwithstanding. But, I suspect that it is in fact the correct listed rad for your car.

I would get rid of the wire, period. It's a brutal hack that is typical of wiring "modifications"; done by someone who doesn't really understand what they're doing. It's bad for the car, the way it's done, and needs to go, before it causes other problems.

These cars' cooling systems work just fine in stock trim if properly maintained (leak-free, full of coolant, all parts working). If it doesn't work right, it needs to be repaired, not hacked.

 

Okay,
Today I was able to go out to my car and just for sh*t's and giggles take a good look at my radiator. Just about 3 inches above the lower radiator hose, I found a small 9/16" hex head brass plug in the radiator about where your sensor is located. Does your car have the stock gauges in the instrument panel or has someone added some aftermarket gauges for the Tachometer, Voltage, and water temperature by any chance. If you want to remove that sensor, you can get a brass plug to put in the radiator from the dealership or a junkyard.

 

As far as I can tell, the car is all original (aside from that extra fan wire) - no extra gauges or anything that I can tell. The only "mod" the previous owner told me was that he installed a 160 Thermostat and a "race/hi-flow" water pump - he didn't mention anything about the fan. I took this as he had problems/was worried about overheating.

From what I've gathered/assumed is that he probably also replaced the radiator from one that was pulled from a junk yard that had this sensor already attached.

I guess as long as the sensor is not causing any problems, I'm just going to leave.

I am definitely going to remove that wire to try and get the fan control back to normal.

Now I just have to find matching bolts (trying to keep it all original) to mount the fan relay back onto the sheet metal .......

Thanks for all the info and help.