Question-------------------------
Followup To
Question - Roland: Would you resubmit your answer to my followup, It appears that the two answers I received from you today are the same, beginning with "A dark blue wire...". I didn't receive your first answer to my followup(giving you the coded numbers). Thanks, Alan.
-------------------------
Followup To
Question -
!990 Dodge D-150, 5.9L, A/C, 110k miles, (no additional accesories or packages). The voltage gauge drops to 10V, ocassionally will jump back to 12V, but then falls back down to 10V. The alternator has been replaced and a new battery! Is it the voltage regulator within the SBEC($$$$) or something else? Please Help. Thanks.
Answer -
Hi Alan,
Before concluding that there is a problem with the voltage regulation function of the SBEC, I would suggest that you do a readout of the SBEC to see if it has stored any faults in the charging system as coded numbers. Here is how to do it:
Turn the ignition key as follows: off-on-off-on-off-on and leave in the on position (where "on" is the normal run position, and do the switching process in less than 5 elapsed seconds). Then watch for the check engine light to begin to flash, pause, flash, pause, etc. Count the number of flashes before each pause and make a mental or written note. The last two groups of flashes will be 5 in each. Then pair up the numbers of flashes in the order they came out sp as to form two digit numbers, e.g. the last number so formed will be 55 (which is the code for "readout is completed"). You can repeat the readout to verify that you saw the number of flashes accurately.
It might be the SBEC, but it also could be a wire in the circuit and perhaps the fault code will tell us what it has seen. Let me know what fault codes you read out.
Do you have a simple volt-ohmmeter for testing?
Roland
Roland: Here are the readouts from the SBEC. - #35, #37 & #55 (I did it twice to verify). I don't have a volt-ohmmeter, but can get one if needed. Thanks for your quick response. Alan.
Answer -
Hi Alan,
In my response I said,
"A dark blue wire is supposed to have 12V on it when the battery is reconnected and the ignition switch is in the "on" position. So reconnect the battery and check that out, again shaking harness for a possible loose connection."
I just remembered that the 12V on this dark blue wire is derived from the autoshutdown relay being energized, and that only happens for about 1-2 seconds in the 'run' position UNLESS the engine is then started and is actually running. (This is a safety feature so that if there is an accident and the engine stops running that all voltages and fuel is cut off to prevent a fire.) So you probably will need to get the engine running first, then check to make sure the 12V is solidly present on this wire when the engine is running. If the output voltage on the dash gauge is flakey while the engine is idling, then do this test by just pulling the wire's connector off of the alternator (or if the post for the wire is accessible to the probe tip leave it connected) and put your voltmeter between the wire side of the connector (or the post) for that wire and ground and observe for 12V to be present. Of course disonnecting the plug (if you can't tap the lead to the post itself) will temporarily disable the fiel coils of the alternator, but what is relevant is that the 12V should be rock steady. Shake the harnesses as before to try and get it to be intermittant. If the output of the alternator doesn't drop to 10V except when you are driving, then you may need to do this measurement while you are moving which would require extenalizing the location of the voltmeter so you could see it while you are driving, which may be a bit of a challenge.
Roland
AnswerHi Alan,
The internet ate my homework!
In any case, the codes are not revelatory of anything regarding the charging system. The first one says that there is something amiss in the cooling fan circuit (any reason to suspect your fan isn't coming on when needed, if so that might be of some significance say if that circuit were overloading the charging system due to a short of some sort? You can check it out by pulling the plug on the coolant temp sensor which ought to be somewhere near the thermostat housing; when you remove the plug on that sensor the fan switches on automatically if the circuit is ok.) The second number says the the solenoid for the torque converter to lock up isn't doing its job, but that could be a default code in the case where you don't have a lock-up feature on your transmission, which is possible on an engine of that size, but I can't be certain.
55 code is to say "end of readout"
So we are left wondering why the voltmeter reads low (and I would presume that you are noticing your lights are dim and the engine is getting slower to turnover witht the starter motor. I make this point because the gauges on the dash aren't all that well calibrated.
My suggestion is that you check out the 4 wires that are connected to the alternator. I would begin by disconnecting the battery so as to avoid a short. Then the four wires:
The heavy gauge black wire is a ground and it should be firmly ties to the - clamp of the battery. So with your volt-ohmmmeter, in the ohmmeter mode measure the resistance between those two points at either end of the black wire; it should be close to 0 ohms. Then shake the wires and harnesses to see if you can make it jump off of 0.
The heavy gauge black/gray wire goes to the + post of the battery and thru a couple of disconnects along the way so check the ohms between that wire and the + clamp at the battery that you had removed earlier. Then shake the harness and the torpedo shaped disconnects that you can find to make sure they aren't flakey as read on the meter.
Then there are the two lighter duty wires:
The dark blue should have 12V.... (you already saw this part of the response, you will need to reconnect the battery clamps to check out the functionning of this wire with your voltmeter portion).
The dark green wire is the one that is controlled by the SBEC which you wondered about replacing. So I would go back to the ohmmeter tester, and measure the resistance between the end of the wire at the alternator and the other end at pin #20 of the 60 way connector at the SBEC. To find the pin at that plug, hold it horizontally with the pins facing you and the short tab "up". The pin #20 is the one at the right hand end of the top row of 20 pins. See if you get 0 ohms between those two points, and shake the harnesses and also shake a rectangular black-color disconnect with 10 wires located behind the battery thru which that wire passes to get from one end to the other. That is the wire which causes the voltage regulation by oscillating its voltage between 12 and 0, and so if it had a flakey connection the meter on you dash would jump around as you describe.
If it all checks out fine, then the two choices are:
take it to an auto electric repair shop and see if they can find the cause, or go to a wrecking yard and find a '90 vehicle with the same engine as yours as get its controller and see if that fixes the problem. I wonder if there might not be a short that is dragging down the voltmeter, and a shop might find that for you (such as the fan circuit, if it is bad)
Let me know what you determine.
Roland
