Mechanics

98 GRAND P1478 (BATTERY TEMP)

1998 Plymouth Voyager

Electrical problem
1998 Plymouth Voyager 6 cyl Automatic 100000 miles

i hav a p1478 fault code. Which is battery temp. Out of limit.I cant seem to locate the battery temp. Sensor. Is it internal of the pcm.I checked the charging volts at the battery with a charging system tester and it bounces between normal charing range to over charging. Can a bad alternator cause this fault?The alternator does hav a little whining noise coming fromit also. My coolant temp gauge on the dash doesnt work either unless im driving for an hour or so. And I let it idle in park or drive(but not moving) the temp will jump to normal operating range. Dont know if its stuck open thermostat or bad coolant temp sensor.I do seem to get heat 10 mins after initail start from cold eng? Any input apprec.
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Joeproe
December 11, 2009.



The battery temperature sensor lives in the PCM where intake air blows over it. The assumption is the air is the same temperature as the battery. As I recall, there is some other problem that causes this code. The computer expects this sensor to report the same temperature as another sensor after the engine has been sitting for a while and has cooled down. Maybe someone else can refresh my memory.

The best way to check the charging system is with a digital voltmeter right across the two battery terminals while the engine is running. The voltage must be between 13.75 and 14.75. Too low and the battery will not fully charge while driving. Over about 15 volts and water will start to boil out. Some inexpensive alternator testers pick up the ripple caused by the alternator's three phase output and interpret that is an intermittently too high voltage.

There are two coolant temperature sensors. One, with a pair of wires is for the engine computer. You need to find the other one with a single wire, usually purple. You didn't list which engine you have. On the 3.0L, it's near the thermostat housing. If you unplug that wire and ground it with a piece of wire, the temperature gauge should go to full hot when you turn on the ignition switch. If it does, suspect a problem with that sensor. Ford has had a real lot of trouble with coolant temperature sensors for the engine computer, but Chrysler has very little trouble with either of their sensors.

If the gauge stays on cold when the wire is grounded, that leaves out the sensor as the cause. Don't try to shock it into working. You want to keep it dead so you can carefully look for the cause. First of all, push very slowly on the display lens while watching the pointer. If you see the needle jerk a little, then start to move up, suspect there is a loose connector pin on the back of the cluster. Pressing on top of the dash might affect it too.

Next, try lightly tapping in front of the gauge. My Dynasty with only 4,000 miles has an oil gauge that intermittently stays on zero until I tap on the lens. Driving over rough roads won't shock it enough to get it started. I haven't autopsied it yet, but the mileage is too low to have loose connector pins. I don't know the cause, but I'm pretty sure it's a problem with the gauge itself. It's also possible the pointer is sticking on something. On older cars, the plastic laminate with the numbers printed on it could shift position a little when the glue softens in the hot sun. This was common on Daytonas, but our gauges have a hard plastic front that can't shift position. My best suggestion for now would be to find a different gauge in the salvage yard.

Caradiodoc

Caradiodoc
Dec 12, 2009.
Hey thanks for the reponse. Ill check out your sugg. The eng. Is a 3.3L. Your right about another sensor. Cause when the eng. Is cold it starts and stumbles or stalls for a moment tthen the battery light comes on and it smooths out. Also I used a snapon battery load/charging system tester and when I turn on the headlights you can see them gradually getting brighter then they dim and that continues bright/dim/bright. Dim and it shows on the tester also?

Tiny
Joeproe
Dec 12, 2009.