Last week I bought a TJ Executive sedan with 240k on the clock as a spare car, and for my son to learn to drive on. Was unloved but it had full service history up to 220k (inc timing belt).

Changed the oil to Penrite, it had Gulf and Western in it.

Cleaned engine bay but is now throwing a CEL, which disappears after about 10-30 sec of driving.
Looked through the forum to ascertain how to read the error codes and found Max’s FAQ (thanks) and also looked at the workshop manual. Connecting Pin 1 to pin 5 and then read the flashes long and short seems to be the easiest way to go.

My question is about the pinouts of the plug. Which one is Pin 1?

I can’t find a diagram of the pinouts for the plug (unless it’s exactly the same as an OBD2 plug). Is it the same as this? http://ww2.justanswer.com/uploads/superbovine/2011-09-27_231453_capture.jpg.

Sorry if this is a dumb question, I’m just cautious about shorting plugs out when I'm not completely sure. :confused:

One other thing I found is that the output of the alternator is about 15V which seems to be high, this may be part of the issue.

Thanks
Ron

Found the pinout diagram - thanks (must be going blind in my old age). One question remaining is 15V too high an output for the alternator.

Found the pinout diagram - thanks (must be going blind in my old age). One question remaining is 15V too high an output for the alternator.

In theory, 14.4v is the perfect score for an alternator.
Why? You ask?

12v is the output of your car battery. Lead-acid batteries also have an internal resistance which must be overcome (galvanic resistance) to initiate charging. This internal resistance requires 0.4v per cell to overcome. The 0.4v is obtained by using Ohms law, where the current required to overcome the resistance is directly proportional to the voltage that must be applied...ie...Current = voltage divided by resistance.
As there are 6 cells in your car battery, (count the filling holes on your battery, there will be 6 ie 1 per cell) that makes the total required for initiating charging 6 x 2.4= 14.4V
So, in short, I do not believe 15v to be too high.

"........ but is now throwing a CEL, ......."


WHAT ???????

Hi jdisnow.

15V is towards the safe upper limit. Is it 15.0 or 15.9?

Typically it will be higher initially once started and will slowly drop off back towards 14.2 or so once the battery is charged.

Take it for a good drive and then check the alternator voltage, it should be well below 15v.

I make it a regular habit to check voltage across the battery and to be honest, seeing 15V on my digital multimeter would worry me a lot.
I'm assuming your multimeter is accurate of course - what does it read with the engine off?

15 volts on the multimeter is within the acceptable range.

But the reading depends on various conditions (RPM, temp, SOC, rate of chemical reaction, SG etc).
If it stays at 15 volts (2.5volts/cell) with driving I'd be looking for issues (as this could lead to overcharging the battery).

PS:
Batteries are undergoing the chemical reactions of charging or electrolysis whenever you are putting in more energy than that lost by self discharge and heating (heating is due to physical internal resistance).
There is no rule that says you need an extra 0.4 volts per cell, on top of the OC voltage, before the battery will accept charge.
The battery will sit at whatever overvoltage is needed at a particular input current.
It takes very little to overcome self discharge (a few 10's of milliamps!) so you could be charging at 100 milliamps with just enough overvoltage to exceed that required to start the chemical reactions at the anodes/cathodes.
EG:
A fully charged flooded battery is typically floated at 2.25 volts/cell (just maintains full SOC).
Same battery, but partially discharged, will take a fair charging current at 2.25 volts/cell (only 0.25 volts/cell above OC potential!)

Thanks for the replies, I thought 15V may be too high for some of the circuitry. It was measured when the engine was warmed up and had been driven for about 30 mins. It didn't change with the headlights on or off either as well (I'm not sure it should have?).

Max, I 'll grab another multi-meter from work to check the voltage with the engine both on and off. I was testing at idle speed with A/C on, and headlights on and off (inc high beam).

I'll try again ................

"........ but is now throwing a CEL, ......."


WHAT ???????

CEL is a 'check engine light' on the dashboard.

Yep 15V is high, replace the diode pack in the alternator - cheap and easy to do, this will likely make the CEL go out as sensor voltage ranges and/or the computer are out of the acceptable range as the voltage is too high

Thanks for the info, was my gut feel but nice to have it confirmed.

If there is a bad diode in the trio pack, it won't change the "alternator" output voltage.
It just increases the ripple current on the battery (don't know if that is sensed!).

Bus voltage is controlled by field current regulation on the alternator rotor.
As mentioned, the Alternator/Battery voltage typically settles somewhere around the 14.4 volt mark.

There are various factors that adjust that set point though.

Maybe check the regulator?

The diodes also act as zener's to limit the output voltage of the alternator without the presence of the battery (battery = stiff supply).