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Donny
Donny, ASE Certified Technician
Category: Car
Satisfied Customers: 827
Experience:  A.S.E. Master Technician, Over 25 years working in Chrysler dealers, Top tech DaimlerChrysler 1998
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2000 jeep grand cherokee: gauge..14 v or over ecm..injectors..chrysler

Customer Question

ok i have a 2000 jeep grand cherokee at my shop with the 4.0 the batt gauge stays at 9 volts and the batt is fully charged it runs but poorly ive checked all the powers and grounds at the pcm all is ok ive even replaced the ecm no luck on my scanner there are no codes and battery voltage reads 0 while running voltage at the batt is 14 v or over ecm is commanding alt to full field and injectors wide open to compensate for the low voltage and yes 2 scanners communicate and have basically the same readings otc/snap on ive tried to find wiring diagrams from the amp gauge out but every thing is very vage even on the chrysler site ive also diconnected every sensor on the engine looking for a pull down but no luck there either        HELP!!!!!!!!!!    thanks ken
Submitted: 6 years ago.
Category: Car
Expert:  Donny replied 6 years ago.

Hello

The Jeep does not truly have an Amp gauge or true Voltmeter, all the information like that is sent over the PCI BUS to the cluster from the PCM if the PCM is reading zero volts the 9 is most likely just a place keeper for the cluster,

From what you are describing you have lost battery sense to the pcm, you will need to check pin 25 in the c3 PCM connector(light blue with red wire) for voltage while running back probe should be what the battery is reading this is the gray 32 way connector, also you will need to check pins 2 (orange with dark blue) and 22 (red with black) in the c1 connector at the pcm black 32 way if any of these do not read battery voltage you will need to back trace the wire for a break or large amounts of corrosion

Check around the PCM and its mounting where all the different connectors are

I hope this helps and gets you on your way

If you need more information just let me know

Thank you

Donny

Donny, ASE Certified Technician
Category: Car
Satisfied Customers: 827
Experience: A.S.E. Master Technician, Over 25 years working in Chrysler dealers, Top tech DaimlerChrysler 1998
Donny and 4 other Car Specialists are ready to help you
Customer: replied 6 years ago.
hi thanks but i have already checked those voltages and everything is ok i have even run a jumper backprobing to 12v on each of those wires and still no voltage
Expert:  Donny replied 6 years ago.

Hi

So you overlaid your own wires and it is still full fielding the alt?

Have you run the no fault charging diagnostic tree?

Possible causes

B (+) CIRCUIT HIGH RESISTANCE

GENERATOR GROUND HIGH RESISTANCE

B(+) CIRCUIT HIGH RESISTANCE (1.0 VOLT)

GENERATOR BELT OBSERVABLE PROBLEM

GENERATOR FIELD TERMINAL INTERMITTENT PROBLEM

TROUBLE CODES PRESENT

TROUBLE CODES PRESENT 2000 RPM

PCM (CHARGING SYSTEM NO CODE)

1 Turn ignition off.

Note: Battery condition must be verified prior to this test.

Inspect the Generator Belt tension and condition.

Is the Generator Belt OK?

Yes Go To 2

No Repair as necessary.

2 Start the Engine.

Turn on all accessories.

Raise engine speed to 2000 RPM for 30 seconds then return to idle.

With the DRB III read DTC's.

Are there any Charging System Trouble Codes?

Yes Refer to SympXXXXX XXXXXst for problems related to Charging.

No Go To 3

3 Ignition On, Engine Not Running

With the DRB, actuate the Generator Field.

Using a 12-volt test light, backprobe the Generator Field Driver Terminal at the back

of the Generator.

Note: The test light should blink On and Off every 1.4 seconds.

While monitoring the 12-volt test light, wiggle the Field Terminals back to the PCM

and ASD Relay.

Was there any interruption in the normal cycle of the test light?

Yes Repair the wire where wiggling interrupted the voltage cycle.

No Go To 4

4 ignition On, Engine Not Running

With the DRB, read trouble codes.

Are there any charging Systems trouble codes?

Yes Refer to SympXXXXX XXXXXst for problems related to Charging.

No Go To 5

5 Turn ignition on, engine not running.

Using a Voltmeter, measure voltage between the Generator B(+) Terminal and the

Battery (+) Post

Caution: Ensure all wires are clear of the engine's moving parts.

Start engine.

Is the voltage above 0.4 volt?

Yes Repair the B(+) Circuit for high resistance between the Generator

and Battery.

No Go To 6

6 Start engine.

Warm the engine to operating temperature.

Caution: Ensure all wires are clear of the engine's moving parts.

Using a Voltmeter, measure voltage between the Generator case and Battery (-) Post.

Is the voltage above 0.1 volt?

Yes Repair Generator Ground for high resistance, Generator Case to

Battery (-) side.

No Go To 7

7 Ignition On, Engine Not Running.

With the DRB, read the Battery voltage and record the results.

Using a Voltmeter, measure Battery voltage B(+) to B(-) Terminal and record the

results.

Compare the two voltage readings.

Is the voltage difference less than one volt?

Yes Test Complete.

No Go To 8

8 Ignition On, Engine Not Running

With the DRB, read the Battery voltage and record the results.

Turn Ignition off.

Disconnect the PCM.

Note: Check connectors - Clean/repair as necessary.

Turn Ignition on, with the engine off.

Using a Voltmeter, measure the Fused B(+) at PCM Connector.

Is the voltage within one volt of the DRB recorded reading?

Yes Go To 9

No Repair the B(+) Circuit for high resistance between the PCM and

the Battery.

9 if there are no possible causes remaining, replace the Powertrain Control Module.

View repair options.

Repair

Replace the PCM.

I dont think you will need nine as you already tried it, the only other thing I can think of is the crank sensor,I have seen gauge issues and charging issues caused by these even though the car runs

Donny

 

Customer: replied 6 years ago.
hi donny day 3 still no sucsess all new cam crank and coil pack ive disconnected every sensor on the truck i think i want to try another computer again i am going to try a used one this time if i plug a used computer from a dakota in the gauge works fine but wount start for obvious reasons the computer i recieved from the dealer says it needs to be programmed which we havent had done but the gauge should still come up even though its not programed right? one difference with these new parts is it does run better now it starts right up but still doesnt run right on start up it sounds like it has a big race cam then smooths out
Expert:  Donny replied 6 years ago.

Hello

Be careful swapping computers around since if one car has vehicle theft and the other one does not, if you put the one that does not into the car that does it can learn the theft system and then when you put it back in the car that does not it will not work and will need to be replaced it can also teach a Body controller theft and that may also need to be replaced

If the Jeep you are working on has a chip key, then you have to have it programed as soon as you install it all the secret key information has to be moved from the security module into the engine control module and keys may need to be reprogramed or replaced,if you install it but do not turn the key to the start position all the gauges, etc. should work, if you cycle the key too many times you will lock the controllers down, any more then 2 key cycles can cause it to lock out, so if you try it you will need to unplug it and either put the original back in to drive it to have it programmed, or leave it unpluged and tow it and have them plug it back in too program it, if no chip key or alarm you can install it and drive it over so they can put in the VIN and mileage

Have you run a cluster self diagnostic, I know that with a DRB3 you can force the cluster to run a self test which would tell you if it was having any internal or communication issues, I am not sure if you can do this or not with your test equipment

Try this and watch the gauge for a full sweep if you cant run a self test with your scanner

1. With the ignition switch in the off position, depress and hold the odometer-reset button.

2. Turn the ignition switch to the run position, continue holding the odometer reset button until the cluster needles start to move, then release the reset-button. (Do not allow the ignition switch to enter the start position) The gauge needles will sweep in both directions and come to rest in the correct position relative to the stop peg.

This will at least tell us if the cluster is capable of displaying higher then 9 v

Let me know what happens and if you need more information

Donny

Customer: replied 6 years ago.
hi yes i have done the cluster diag and all the gauges do sweep including the amp gauge the computer i was using was one we had as a test dummy so there was no other vehicle involved   i believe the cluster is ok when i put the ecm from the dodge truck in to see if the gauge came up it did and read batt voltage
Expert:  Donny replied 6 years ago.

Hello

Well after having checked and verified all the wiring and connections like you have done and seeing the cluster be able to display more then 9 volts, I would say that it most likely is the engine controller, the only thing you may want to do first is verify the controller grounds by putting them under load, i normally do this by using a light bulb (fog lamp bulb) hook a jumper wire up to B + and then to one side of the bulb and then hook the other side of the bulb to the ground pins of the engine controller connector one at a time and be sure the bulb is bright, some times an ohm meter can show good continuity to ground but when current is flowing the ground is not good, if this tests fine then the controller is most likely bad

Pins 31black with white and 32 black with tan of the c1 black connector

If you need more information just let me know

Thank you

Donny

Customer: replied 6 years ago.
hi don thanks for all your info i have a yard computer comming tommorow i will try that and let you know how i make out youve been great thanks ken
Expert:  Donny replied 6 years ago.

Hello

If by yard computer you mean a used computer from a salvage yard, it will not run the Jeep if the Jeep has the chip key or factory theft system, once the computer is programed with the VIN it cant be overwritten or changed to a different vin, if the Jeep you have does not have one or both of these systems on it you should be able to use it,

Donny

Customer: replied 6 years ago.
hi don ok the used computer did the trick the gauge comes up now and the truck runs for a few seconds before the sec system shuts it down but when it does run it runs normal i ordered another reman one from chrysler then i will have it programed
Expert:  Donny replied 6 years ago.

Hello

Thats good to hear, then you should be all set once the reman is programed to the jeep

Take care

Donny

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