Volt meter

[OurPTGT]

What should it be sitting at idle? mine WAS staying at 14 constantly, whether at idle or while driving with or without load. Thanks
KB

[Dalite]

The Low Voltage test (P0562 - Battery Low Voltage) is measured at RPM greater than 380 RPM. It is considered low voltage when the battery voltage is less than 11.5 volts for 10 seconds. This will cause the battery lamp to illumunate. The Battery Lamp will turn off if the battery voltage recovers to 12.04 volts or greater, due to reduction of load, increased RPM or an intermittent condition.

The P-0563 Battery Voltage High error is monitored at engine RPM greater than 380 RPM and is considered to be high voltage when the Battery Voltage is 1 volt greater than desired system voltage.

The above is from the 2003 Powertrain Diagnostics Manual.

The P-2053 - Charging System Voltage Low error testing shows 15.1 volts as the normal charging voltage, with the battery sensed voltage 1 volt below the charging goal for 13.47 SECONDS to be an error.


I think the "normal" system voltage is around 13.8 volts, but can't find confirmation in the manual. From what the above shows (not much) I would think that 14.0 volts would be OK. If it is too high, there are a number of ways for the PCM to get this info. It is monitored at battery voltage and battery temperature; both will alert the PCM to look for signs of over or under charging.

Was this measured on an analog gauge, or a digital voltmeter? If on an analog (dial and needle) one, then 14 could be 13.5 to 14.5 (or possibly a wider range) volts.

Based on old technology for battery sales, a battery shouldn't go into service if it measures below 12.53 volts, but the real way to check it is to have it fully charged, verified by specific gravity measurement and then load tested. Today's sealed batteries prevent specific gravity testing, so we have to leave that up to the PCM to determine by other ways.

If it is not causing any error codes, I wouldn't be too concerned about the 14 volt reading; especially if read from an analog gauge.

[OurPTGT]

Thank you kind sir. Your responses never cease to amaze me. If one can't find the answer in your responses, there must not be one.[?] It was indeed a dial/needel type (Autometer) As I said, it USED to be rock steady at 14. Now it fluctuates between 13 & 14 depending on load AFTER installing a underdrive pulley. I just wanted to be sure 14 was OK to begin with. Thanks again Mr. D[|)]

[Dalite]

Kevin,

No problem. I just try to put as much info as I can from the manuals. That is why I got them, primarily to better understand things and to try to help others. Every time I try to help with an answer, I learn a little more, and that is a lot easier way for me to learn the systems than to just read the manuals.

The underdrive pully may tend to spin the alternator a little slower. From what I understand the water pump is not belt driven (not sure about this). The way the PCM controls the charging rate is by "pulsing" the field of the alternator when the data it receives tells it to do so. In this way, the more often it pulses, it apporaches steady voltage to the alternator, while apporaching steady charge. The underdrive pully may increase the pulse rate over that of the standard pully due to the slower speed the alternator is being turned. As long as it is turning above 380 RPM to 1125 RPM at idle, it is supposed to be able to provide full charging to the battery.

The battery temperature sensor that is located under the battery tray also tells the PCM if the battery is being charged too rapidly (battery heats up) and the PCM will respond to that by slowing the pulse rate until the battery returns to normal temp.

The short answer - as long as you don't receive any of the error messages listed in the other reply, you should not have a problem.

Enjoy,

David

[MX-5]

quote:Originally posted by Dalite

The battery temperature sensor that is located under the battery tray

Don't mean to but in... but.....
I've seen posts about the battery temp sensor under the tray. I don't know where that came from.

Here's page 8F-23 of the 2002 manual:

BATTERY TEMPERATURE
SENSOR

DESCRIPTION

The IAT sensor attaches to the intake air duct
(Fig. 1).
The IAT Sensor is a Negative Temperature Coefficient
(NTC) Sensor that provides information to the
PCM regarding the temperature of the air entering
the intake manifold. The PCM sends 5 volts to the
sensor and is grounded through the sensor return
line. As temperature increases, resistance in the sensor
decreases.

OPERATION

Inlet/Intake Air Temperature

The inlet air temperature sensor replaces the
intake air temperature sensor and the battery temperature
sensor. The PCM uses the information from
the inlet air temperature sensor along with other
stored parameters to determine values to use as an
intake air temperature and a battery temperature.
The IAT sensor value is used by the PCM to determine
air density.
The PCM uses this information to calculate:
² Injector pulse width
² Adjustment of ignition timing (to prevent spark
knock at high intake air temperatures)
Battery Temperature
The battery temperature information along with
data from monitored line voltage (B+), is used by the
PCM to vary the battery charging rate. System voltage
will be higher at colder temperatures and is
gradually reduced at warmer temperatures.
The battery temperature information is also used
for OBD II diagnostics. Certain faults and OBD II
monitors are either enabled or disabled depending
upon the battery temperature sensor input (example:
disable purge, enable LDP). Most OBD II monitors
are disabled below 20°F.

[Dalite]

I should have mentioned that was info for the 2003 model.

I am fairly sure that it is located under the tray on the '03 model, but I could be wrong....

It may not even be an important factor, as I have heard of others remoting the battery to the rear for weight distribution and custom intake systems...

[MX-5]

David,

You are correct.
I own 2001 & 2002 PTs.
Here's the info from the 2003 manual, page 8F-25:

BATTERY TEMPERATURE
SENSOR

OPERATION

The battery temperature sensor is used to determine
the battery temperature and control battery
charging rate. This temperature data, along with
data from monitored line voltage, is used by the PCM
to vary the battery charging rate. System voltage will
be higher at colder temperatures and is gradually
reduced at warmer temperatures.
The sensor is located on the bottom of the battery
tray, and makes contacts with the bottom of the battery.

[Dalite]

MX-5,

No problem here. I value the time you have put in "in the trenches" on the 2001 and 2002 models. If it weren't for folks like you and Bob Stockum, we would never have known much of anything about the 01s and 02s, and just what they were capable of. I am trying to get into the PCM part of the 03 GT and get an understanding of just all that it does. Maybe one of these days we will get a data logger that can fully talk to the next generation controllers that are on the 03 model, and get an idea of just what all it is capable of.

FWIW, the Stage II prototype for the PT GT is giving 260 hp with just PCM, Injector and surge actuator changes. 45 hp through electronics, fuel delivery and boost control is kinda hard to believe, but apparently the engine has it to give.