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mhall1019

No windows, sunroof, interior lights, central locking, etc, Part II

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This is Part II of the process of trying to find out why fuse C3 blows as soon as I put the fuse in. This disables the things in the title and prevents the doors from locking other than the driver's door with the key. Story started August 13.

So far I have done the following (some unrelated) without finding the solution:

1) Checked battery, voltage was low (12V) due to low output from alternator; changed voltage regulator. Now runs about 13.5 volts. Bad battery is apparently main cause of alarm logic failures. Replaced both oil temp. senders.

2) Looked at wiring diagrams which led me to fuse C3 which was blown. Replaced it and things lit up. Shortly thereafter fuse C3 blew.

3) Removed seats and checked the condition of alarm logic box on driver's side. Disconnected airbag connectors on both sides. Replaced fuse C3. Everything worked. Put airbag connectors back together and everything still worked.

4) Removed headliner.

5) Put seats, etc. back in. Fuse C3 blew.

6) Bought PST2 laptop clone on eBay. Learned something about it and troubleshooting with it. Found out about Diagnostics Manual that was sitting right on my computer. Learned about IPAS codes which are required to activate and teach modules (e.g., "program" new key). Dealers are reluctant to give people their codes even after showing proof of ownership because they don't want to lose out on the money if people fix their own cars. There is also a security issue. But, there are dealers that will provide the codes. You just have to find one.

7) Replaced Passenger Compartment Sensor (senses presence of either kind of passenger - driver or passenger) and central locking switch. Fuse C3 blew.

8) Left front turn signal stopped working. Changed bulbs, worked on socket for about two hours. No help. Swapped sockets/lamps left to right. Problem followed socket/lamp. Right turn signal now not working. Ordered two new sockets. Got in car next morning and both turn signals were working and have continued to work ever since. No affect on Fuse C3. Sockets are cheap - $13 and are the major cause of turn signal failure. Turn signal lamps last longer than sockets.

9) Removed fuses D8 & D9 to isolate the removed PCM module from power. No help.

So, almost a month later I am about $1200 (including $50 worth of 15 amp fuses :blush:) poorer and still have same problem.

I am resisting the temptation to buy a new alarm logic module until I've done more testing. The modules aren't cheap, but not outrageous.

The diagnostic manual has whole sets of troubleshooting sequences for each of the alarm module codes. Yesterday, I had alarm logic module codes 34,60,61,47,46,10 &11, I reset the codes. This morning I had just 47, 34, & 60. Later this morning I reset the codes, drove home from the store and still have no codes.

I could go through the diagnostic procedure for, lets say, code 34. However, there are only two solutions for fixing a code 34. One is to replace passenger compartment sensor (already done) and repair wiring harness. So, I need to check wiring harness for problem and repair it - what wiring harness? The two that go to the alarm logic module or the one that goes to the passenger compartment sensor?

For code 47, first check input signals from doors that are not locked. If PST2 indicates Driver's and Passenger's doors not locked (which mine did), check door locks. The following steps include removing connectors from door locks and from alarm logic module, checking continuity between terminals. This means taking door panels off (?) and front seat out. But, the only two options for repair are repair wiring harness or replace alarm module. What wiring harness?

The diagnostics for code 60 are very clearly written but has lots of steps. Since I already know that the central locking switch is not working (but, it is good because its new (?), so I think its not working because fuse C3 is blown) I go to step 5, 6, and 7 or 8 which say to repair wiring harness or to step 9 which says to repair wiring harness and then maybe to step 10 which either takes us to check fuse C3 or repair wiring harness or replace alarm system control module. Step 11 is not feasible because during the few short times fuse C3 stayed closed long enough to lock the doors with the key fob, the doors locked. So, the door locks are OK.

My conclusion is that I should check every wiring harness in the front of the car or replace the alarm system control module.

Maybe I should just buy an alarm system control module.

"Andraya, please ship alarm module".

Mike

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C3 also goes to the central locking switch - try disconnecting the switch and see if it blows.

C3 also goes to the sun sensor (on the dash) - try disconnecting the switch and see if it blows.

Other than the interior sensor and the tilt sensor those circuits are the likely cause.

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C3 also goes to the central locking switch - try disconnecting the switch and see if it blows.

C3 also goes to the sun sensor (on the dash) - try disconnecting the switch and see if it blows.

Other than the interior sensor and the tilt sensor those circuits are the likely cause.

Thanks, Loren, but that can't work. Its too easy. I never bothered to follow the lines from fuse C3 to see

where they went. Is the sun sensor up by the red light that shows the alarm system status?

I'll check them out tomorrow.

I was also thinking about putting a 300 amp fuse in the C3 slot and see which wire melted.

Mike

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I was also thinking about putting a 300 amp fuse in the C3 slot and see which wire melted.

I have personally seen a 996 series car burned from a dash fire - you don't want to do that.

Yes the sun sensor is part of the same assembly.

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I was also thinking about putting a 300 amp fuse in the C3 slot and see which wire melted.

I have personally seen a 996 series car burned from a dash fire - you don't want to do that.

Yes the sun sensor is part of the same assembly.

My first 911 - a '74 that I bought in '84 caught on fire and burned up on my way home from picking it up from the PO. Probably a leak in the oil cooler running onto the exhaust.

Anyway, disconnecting the central locking system button had no effect. Fuse blew right away when I inserted it after disconnecting the cable. But the problem could be in the cable itself, I guess.

After disconnecting the sun sensor, I got a few locks/unlocks before the fuse blew. The cable going to the sun sensor looked scraped up - potential for a short there. I untwisted the wires a bit, tried a new fuse, and I was able to lock/unlock without blowing fuse, but, it got too dark and cold to try to fish the cable down to where I could look at it closely, so I decided to leave it overnight. I probably scraped up the cable when I took out the defroster panels a couple of years ago. The CF just curled up and fell off. I think you really need to take the windshield out to change those panels.

I still have the sun sensor cable to check out and if that's not it, I guess I should check out the other cables getting power through that fuse. I don't have a tilt sensor and siren - I wonder where those cables are tucked away? How likely is it that a cable that is sitting still can have a short most of the time and occasionally isn't shorted?

Since the switches have been ruled out, and the cables are just sitting there, its not likely they have a short in them with the symptoms I'm having.

This acts like a problem with something with moving parts like a relay. Or a device with semiconductors giving up the ghost.

This whole troubleshooting process has been a series of connecting and disconnecting switches, devices and cables and every once in a while the problem goes away for a few clicks of the transmitter, but then the fuse blows. But the same action 5 minutes later doesn't have the same effect.

Just a bunch of thinking out loud.

Mike

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wouldn't a PIWIS diagnostic tool help a bit to isolate the issues? Trouble shooting electrical issues is a major PIA.

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wouldn't a PIWIS diagnostic tool help a bit to isolate the issues? Trouble shooting electrical issues is a major PIA.

I have a PST2 clone, but it doesn't have the meter inputs. I documented a summary of the diagnostic procedures above and, after replacing switches and sensors, the only solutions left are to either " check wiring harness" or "replace alarm logic module". Most wiring harnesses are buried behind heater ducting, carpeting, and generally, a cable, for instance the sun sensor 4-wire cable joins a big bunch of cables behind the middle air duct and in order to "check wiring harness", every other group of wires going into that bundle would have to be removed from their termination points so that the wiring harness could be pulled out enough to be able to check it.

What Loren did in his last response was to point out all the things that got their power from C3. I had already eliminated a couple of the items, so, when I got to the last one, the sun sensor, and pulled off the connector, and the fuse still blew, I was really frustrated. But then I looked at the four wires going into the sun sensor connector and they looked suspicious - like they might have some insulation scraped off. I untwisted the wires and separated them and the problem hasn't come come back for a whole day. If that is the solution, then it was arrived at by using the simple old technique of checking every path of wires to the fuse. If I find out that the sun sensor is important, I will have to pull out more of the wiring bundle that the sun sensor wires is tied into on the way back to the fuse box. If I can replace that one wiring harness going to the sun sensor I could do that, or I could wrap each of the 4 wires individually with tape so if there is a short between two of them, I will insulate them from each other.

If the problem is gone for a week, then I'll start putting things back together and hope its fixed.

Mike

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Impressive research Mike. If the wire is not completely broken and they were only touching each other do not go into the trouble of replacing it. Just isolate it and it will be fine. Do you know if it was damaged by somebody working in the area or if it was only by vibration and rubbing on each other ?

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Impressive research Mike. If the wire is not completely broken and they were only touching each other do not go into the trouble of replacing it. Just isolate it and it will be fine. Do you know if it was damaged by somebody working in the area or if it was only by vibration and rubbing on each other ?

jp- I think I may have done it when I took the defroster panels out to replace the CF trim that had curled up and fallen off. That is a job I wouldn't try again with the windshield in the car. The problem is that I couldn't get the cable out in the open enough to look at it thoroughly. I think I'll just wrap them and hope I can get the cable back up to connect to the sensor. Its sitting in the cavity where the nav system goes and it will be just about impossible to get it back up through the maze onto the top of the dash.

What's the sun sensor for? Can't they just use the clock and see what time it is (adjusted for DST) ;) ?

Mike

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The sun sensor is for the climate control to compensate for the hot sun entering the car. How come I did not have this device in my Datsun 510 1970???? Oh my god I drove this car without it!!!! :D

Edited by jpflip
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The sun sensor is for the climate control to compensate for the hot sun entering the car. How come I did not have this device in my Datsun 510 1970???? Oh my god I drove this car without it!!!! :D

A Datsun 510! Wow, you actually owned one. I used to watch them racing BMW 2002s, Mazda RX4s, and other great IMSA race cars of the day.

Anyway, the same fuse is still running in slot C3. I'll wrap the wires before I put it back together, and we'll make sure it isn't the sun sensor.

Thanks again for your help.

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Mike I am happy you finally found a cure for your problem. Congratulations! :cheers:

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