richrd0001

This is re my '89 Prelude Si -- I'm getting a dead battery overnight.

Initially, I found my A/C condenser fan was starting up and running, even hours after shutting off the engine. I replaced the A/C condenser fan relay and that seems to have stopped the fan problem.

Now there's just a dead battery without the fan running (to my knowledge).

I've not checked my inside fuses, but using my ammeter to do a parasitic draw test on the fuses under the hood tells me this:

1. If I unplug just the A/C condenser fan relay ("the relay"), I get a reading of 4 milliamps between the negative post of the battery and the ground.

2. If I plug the relay back in and connect the ground cable back to the battery negative post, I hear and can feel a click inside the relay. The same thing happens if I don't reconnect the cable but put the electrodes of the ammeter on the negative post of the battery and a bare metal ground on the engine.

3. When I do 2 (just using ammeter leads NOT reconnecting neg. cable), the ammeter reads 162 milliamps.

4. I think the clicking from the relay is not right. As I understand relays, the click is from a small current from a sensor or switch that causes a switch to close thereby completing a high-amp circuit such as to a motor or a head light. When I connect the negative cable to the battery, I am therefore hearing the click because the low-amp circuit is hot but it shouldn't be. I believe from the wiring diagram that the engine coolant sensor is the sensor that energizes the relay thereby causing the cooling fan to come on. BUT . . . the fan DOESN'T come on, whereas it should if my analysis is correct (and there's not some recent failure of the cooling fan).

5. The engine coolant sensor is new and removing the 2P connector at the sensor when the engine is cold doesn't stop the click.

6. The "Clock" fuse under the hood is the one that you remove to reset the computer and erase the stored error codes after a CEL warning. If I remove that and check for current flow I think I get a reading of 26 milliamps [which then drops to 4] but I'd have to double check that as my memory is a bit fuzzy on that point right now [rechecked as above]. Suffice it to say, it's a lot less than 162 milliamps.

7. It seems that the ECU is sending current to the relay, not just the engine coolant sensor. This is possible because Haynes manual wiring diagram shows the A/C Compressor Control Unit is connected to the A/C Diodes, which are connected to a Junction Connector, which is connected to the low-amp circuit going to the relay.

8. A/C was working again early last year but just quit. (Green light and then no light.) I think I need to reflow the solder in the control unit on the dash.

My questions are:

A. Should there be a click when I connect the neg. battery cable and should the low-amp circuit thru the relay be, presumably, energized all the time?

B. Could the ECU be sending a current for some reason to the low-amp side of the relay and, if so, why?

C. Is this (B) causing my battery to be drained or is there some other reason?

holmesnmanny

something is giving the relay power when it shouldn't be so the issue is upstream of that ...im thinking maybe a bad fan timer unit....pull. it and see if it goes away

richrd0001

Good idea. I'll try that. Thank you very much.

richrd0001

Manny, where might the fan timer unit be? I don't see such an animal in the wiring diagram with that name but I do see a "cooling fan control unit" in one wiring diagram (but not another). Could that be what you re talking about? Any idea of location?

The differences in the wiring diagrams are baffling as both diagrams supposedly are for my year and model.

Ooops. I checked a supplement to the manual and I see the "cooling fan control unit" either under the hood above the air filter canister (picture) or under the dash passenger side (text). I will troubleshoot per manual and let you know.

holmesnmanny

http://www.hondapartscheap.com/parts...-fuse-box-horn

part #9

richrd0001

Thanks, Manny. I appreciate your finding that diagram for me. I did find the control unit inside the car on the passenger side. It's behind a panel of "carpet" at the bottom of the door jamb on the passenger side. It's forward of the jamb and you have to pull back that flap of carpet. It has a stiff plastic backing, which I cracked as I uncovered the unit. It seals back up fine even with the crack. First time opened in 24 years . . . .

I've determined that I need to test the TA (air temperature) switch/sensor. Do you have any idea where that sensor is? It's supposed to be on the firewall for an FI engine but I'm not seeing it.

You were right. Unplugging the control unit stops the drain. Ammeter test shows 16 mA after unplugging it, down from 162. I think Eric the Car Guy indicated that anything around .01 A is normal. Maintaining clock and radio settings and checking temperature sensors, I suppose, as well as keeping the ECU ticking over. Just guessing on that.

Power is constantly provided to the unit from the battery so if power is coming OUT of the unit, the unit is either defective or it is getting false data from a bad sensor. There are two sensors that feed into the control unit: engine coolant temp switch/sensor and TA [air temp] switch/sensor. If either switch is closed current flows through and out of the control unit (to ground), presumably causing the fan timer unit to output current to the low-amp circuit of the cooling fan relay and/or the A/C condenser relay.

If the ignition is ON, the engine coolant sensor outputs to both fan relays when coolant tempt exceeds 194 deg. F.

If the ignition is OFF, the TA switch/sensor closes only when the engine compartment temp. exceeds 140 deg. F and this appears to cause the timer unit to output only to the condenser relay and runs the condenser fan for 10 mins., hence the name "cooling fan timer unit."

As I am hearing the condenser fan relay click (close) when I reattach the negative ground cable to the battery, the timer unit (plugged in) is thus outputting to the relay either because it is defective or because the TA sensor is frozen closed (normal open) and making the timer unit think the engine compartment temp is above 140 deg. F when the engine is in fact cold.

My remaining problem is then to determine whether the timer unit is bad or the TA switch/sensor.

A related wrinkle here is that if the timer unit is outputting to the condenser fan relay (thereby causing it to close and complete the high-amp circuit to the fan, the A/C condenser fan musts by bad, though I'm sure it was the fan that was running and draining the battery before I replaced the relay. Another problem for another day . . . .

holmesnmanny

I had no idea the air intake sensor had any control over the fan timer. Normally these are located at the intake manifold itself, either on the driver side of the back of it. The fan timers go bad more often than not. However the intake air temperature and fan switches normally simply just stay open when they go bad. I would guesstimate that those aren't the problem. I actually shoulda had you unplug the fan switch that controls the fans when the ignition is off and that's the one at the front of the car in the housing for the upper radiator hose. You can just test if you want, it should have no continuity when cold. You can also just unplug the air intake sensor and see if the problem goes away.

If the issue doesn't go away when unplugging both then that would probably mean the timer is bad and you can source one i'm sure from a junkyard if one is near you.

1funryd

Richard try this for your troubleshooting technique:
I realize its not specific and you may or may not know how to do this, but thought I would post it anyways.

motoxxxman

some 3g's have a separate air temp sensor at the top of the firewall. I've never seen one in person, but I have seen pics a while ago.

the real question though is which coolant temp switch did you replace? because there are 4 coolant temp sensors/switches...
-the one in the bottom of the radiator is the engine coolant temp switch, which turns both fans on when the radiator gets too hot, only with ignition on.
-single wire sensor on the water outlet is for the temp guage in the dash
-white 2-wire sensor in the water outlet is the engine coolant temp sensor that feeds the ecu for engine running parameters and nothing else
-blue 2-wire sensor in the water outlet is the engine coolant temp switch that operates the fans only when the ignition is off, and it only feeds the body control module (aka fan time control module that you found under the passenger side of the dash). this is the sensor related to your current issue.

also you should know that anytime anything attempts to turn fans on, BOTH fans should be coming on. whether it be with ignition on or off, related to engine or related to a/c, both fans will always work at the same time. if only 1 fan works at any time, something is wrong.

it sounds to me like you have a number of faulty parts. I would start by turning your ignition on, then unplugging the blue coolant switch on the water outlet, then turn the ignition off, then test both fan relays for clicking or drain. if the problem is not there, then the blue switch is the faulty part. if the problem still remains, then the body control module is at fault.

related: does the intermittent function of your wipers work? or do the wipers not work at all, or stay constant when in the intermittent position? because the first part of the BCM to usually fail is wiper function. if your wipers don't work properly, the bcm is most likely fried, meaning your drain most likely lies within the BCM.

P.S. the ecu has nothing to do with the fans. the bcm controls all fan function.

richrd0001

Manny, I've studied on this sensor/switch mystery today. My Chilton Manual and the supplement for the 89 Prelude to the Honda Manual (basic manual for Prelude, supps. for '89, and '90 downloadable here) show at least two configurations for the switches. I've been looking for a separate "TA switch" mounted on the firewall (PGM-FI engine) inside the engine compartment and finding nothing.

Since the basic manual for Preludes doesn't show a TA switch and the later manual supplement for '89s does, I'm assuming that the TA switch on the firewall came later and replaced the engine coolant temp. sensor in the block right below the TW sensor. [Edited. I had this backward originally. Not sure which came first at this point. I guess all that matters is that you know which setup you've got in your own machine.]

That IAT (intake air temperature) sensor in the "air plenum" or in or near the throttle body only has to do with the fuel system and is separate from any cooling fan operation. (This sensor is connected to the ECU.) (Chilton, p. 4-13.)

I'll post a separate reply here to summarize what I think is accurate about the sensors and switches relating to the cooling fans (and instrument gauge.

I don't think engine coolant temp. switch A (or the radiator fan switch at the bottom of the radiator) is my problem. I wasn't getting any current draw with the fuse for the radiator fan in and ditto for when I removed the radiator cooling fan relay. Similarly, I only got a click in the A/C condenser fan relay when I reattached the negative ground cable to the battery and not in the radiator cooling fan relay. From my testing with my ammeter, I'm pretty sure that the current loss that is draining my battery is because the cooling fan timer unit is bad (as you thought) and is outputting current to the A/C condenser fan relay when it shouldn't. The relay is normally open until current is sent through the coil of the solenoid (the low amp side) at the proper time, such as when (a) temp. switch A is outputting to the control unit when ignition is on and engine temp is very high, or (b) temp. switch B (or TA switch) outputs to the control unit when the ignition is off and engine temp is high or very high.

I didn't unplug the temp. switch B initially, but you are right that that's an essential part of troubleshooting. After I figured out why I have no TA switch, however, I did unplug the connector and check continuity on the terminals of the switch and I had no continuity when the engine was cold. This would be correct, because the switch should be open when the engine is cold. As it's the only switch that could output to the control unit with the ignition off, it therefore could not be causing any current to flow through the control unit causing the unit to think a cold engine was in fact hot and therefore needed to be cooled by the A/C condenser fan.

My radiator motor is new, btw, but I think the reason that the A/C condenser fan didn't come on when the A/C condenser fan relay solenoid was tripping is because the fan motor is bad. No fuses blown. (Still the possibility of an open in that circuit between relay and motor, I suppose.)

Sorry for long winded answer but I might as well be as clear as possible about my investigation and reasoning.

richrd0001

Thanks very much for that. That one's a new one on me but that's pretty much true of everything with me when it comes to electrical stuff. I've enjoyed trying to figure out some of the writing diagrams but I confess with some circuits I can't figure out whether they ever hit a ground.

Eric the Car Guy also has a v. useful video on how to find parasitic draws.

richrd0001

Thanks for your reply. You are correct. I confused the coolant temp. sensor (TW sensor) outputting to the ECU and engine coolant temp. switch B. It was the TW sensor that I replaced (which may or may not have been bad to begin with as I only later noticed the broken lead wire). Either a bad sensor or a broken lead caused me to have really hard starting and running till the engine warmed up, but that's another story.

I'm pretty confident that I have identified the A/C condenser fan circuit as the problem circuit. Please see my reply to Manny tonight on that. I didn't take off the lead to engine coolant temperature switch B and check for current flow because I didn't know what it was and was looking for the (non-existent) TA sensor on the firewall. Since I don't have continuity on the pins of (newly-discovered) switch B when the engine is cold, I'm sure that the switch isn't causing current to flow thru the cooling fan timer unit, what I am assuming is the same thing as your Body Control Module (BCM). I thus conclude now that the unit is erroneously outputting current to the A/C condenser fan relay solenoid thus causing the relay to shut when battery power is delivered to the control unit (and cause a click when the negative ground cable is reattached to the battery).

Am I correct that what you are calling the BCM is the same as the cooling fan timer unit I'm speaking of?

No, no problems with my wipers at all. I don't see in the wiring diagram where the wiper circuit is tied in with the cooling fan but I could easily be misreading those diagrams.

I get the impression that you are right about both fans being on or off together in some perhaps later models. There is a table on p. 16-29 of the Prelude Honda Manual supplement for '89s that lays out which fans operate when ignition is on, when it's on or off, and when the A/C is on or off. The only time where only the condenser fan works by itself according to this table is when the TA switch (in this case) is closed because air temp is above 140 deg. F (ignition on or off). If this applies to earlier or later versions I've not seen any such table to that effect. (Btw, on this point, I think that the table is incorrect and has the radiator fan turning on for 10 mins. I believe the 10 mins. should apply to the condenser fan. The two lines should be switched.

PS. I also think the chart on p. 16-33 is wrong in that it indicates there should be continuity at temps below 99-116 deg. F. The TA switch shouldn't be closed when the engine is cold. Just thought I 'd add that in case someone needed to check out the TA switch.

richrd0001

I hope this will be a useful summary of the sensors and sender. Take wire colors with a grain of salt. I've not double checked:

Engine coolant temp. switch A (or radiator fan switch).
Controls radiator fan and condenser fan.
Located in bottom of radiator.
Wires yel/blk (or red for 2.0l)
Ignition on.
Current on (v. high temp.) or off.

Engine coolant temp switch B.
Same function as TA switch which measures temperature of air inside
engine compartment.
Controls A/C condenser cooling fan.
Cooling fan timer unit turns off condenser fan after 10 mins.
Off-yellow connector. Also gray?
Wires wht/grn and blk (grd), maybe ylw/grn and grn/wht??
Ignition on or off.
Current on (high or v. high temp.) or off.
(Honda?) Part # WT5009

Coolant temp sensor (TW sensor).
ECU input.
Also called thermosensor C?
Wires grn/wht and yel/grn.
Blue plastic connector.
Located near thermostat.
Variable signal.
(Honda?) Part # 36426 (WT 36426?).

Coolant temp gauge sender.
Outputs to dash coolant temp. gauge.
Single wire red
Located near thermostat.
Variable signal
(Honda?) part WT622.

Very helpful discussion about cooling fan operation from beatngyu27 here. Some data above from there as well as from Kbulls91Lude here, where you can also learn from the discussion if a body studies on it.

holmesnmanny

lol I figured this was just a 3rd gen thing with the air intake sensor somehow giving input for the fan relay. If you woulda said 4th gen I woulda said that's not possible.

Anyway, I gotta be honest with you, Haynes and Chilton's really suck. When reading them you should almost always just assume it's wrong in more ways than they are correct.

I've never taken off the fan timer but if you have battery voltage output when it shouldn't be then just replace it.

Both fans will work any time the ignition is on when they need to turn on. The only time only one fan will run will be when the ignition is off. At this time only one will run. Can't remember at this moment but I think it's the passenger one.

richrd0001

Yes, I've discovered that those manuals need to be studied carefully. They are invaluable but hardly perfect.

I got a control unit off of a 1988 Prelude with a B20 engine. Same configuration of sensors and switches. Part no.:

TL-23 7.D 261
47740-PJO-662 (P-J-oh) or 47740-PJ0-662 (P-J-zero).

Circuit board inside no. is F2M-85086. Also has numbers TL-23 and
CMK then underneath
3 (inside circle) and "NN", "MM", "HH", or symbol of two diodes (inside circle).

I'll let you know if it works.

motoxxxman

yes, the BCM (body control module) is the cooling fan timer and intermittent wiper timer.

richrd0001

Thanks for confirming.

richrd0001

I installed the '88 timer unit and I have no more power output to the A/C condenser fan relay when engine is cold. No clicking of the relay when I reattach negative ground cable. Amperage from negative terminal to (unhooked) negative ground cable only 16 mA.

I'll find out if the A/C condenser fan comes on when it should next time the engine gets hot enough to trigger it.

The part no. for my (bad) '89 cooling fan timer unit is:

TL-23 8.7 072
47740-PJO-662 (P-J-oh) or 47740-PJ0-662 (P-J-zero). I think it's probably (P-J-oh).

Thanks for everyone's help. As always, I'm impressed by the willingness of strangers to help on these forums.

holmesnmanny

nice to hear u got it taken care of