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Cat 257B with battery drain issue. turn key on d+ terminal…

Customer Question
Cat 257B with battery...

Cat 257B with battery drain issue. turn key on d+ terminal shows 1.6V. Start engine alternator produces 14.5V. turn engine off and battery voltage still avail at d+ terminal (batt voltage - 1V) disconnect battery - cable, wait 10 seconds and draw disappears. without disconnect battery overnight will draw battery down to 7-9 VDC?

Mechanic's Assistant: What is the complete model and serial number of your machine?

CAT0257BPSLK06904

Mechanic's Assistant: Anything else you want the construction mechanic to know before I connect you?

Have changed batteries, alternators, checked diodes. removed all fuses, relays. replaced key switch

Submitted: 3 months ago.Category: Construction and Road Equipment
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Answered in 1 hour by:
3/31/2018
Mechanic: catmastertech, Technician replied 3 months ago
catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2,546
Experience: Field service technician for CAT 19 years.
Verified

Hello,

Have you checked the amperage draw from the battery?

Does your machine have any add-on attachments that use power?

Is this equipped with Product link or the CAT MSS security system?

Normally the issue is the alternator, did you replace it with a CAT part?

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Mechanic: catmastertech, Technician replied 3 months ago

I would recommend you try disconnecting the following items by removing the fuse to see if the amperage draw will drop when each fuse is removed. This may help isolate the circuit.

F25 HORN

F23 KEY SWITCH

F22 A/C

F24 MISC POWER

F17 HEATER

The cold start relay and the start relay on the engine.

Each of the relays on the left side of the engine bay. You could have up to four relays.

These relays all use a battery power feed to supply power to the controlled circuit.

Also, look at you harnesses for a damaged area where a wire may be pinched and shorting to another circuit.

NOTE: Most battery feed wires are red and marked with numbers from 100 to 119. CAT does have a few exceptions though.

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Customer reply replied 3 months ago
Amp draw is about 97ma
No attachments
No link, no mss present, C19 connector exposed in cab harness, but no exciter attached, clock display is always on?
Work is at alternator shop, previous alternator disassembledo diodes checked, reassembled, turn off d+ power and no drain.
Customer reply replied 3 months ago
F16 fuse removal results in 50% drop in draw, but does not effect voltage at d+terminal. Main power relay (A) eliminates draw
Mechanic: catmastertech, Technician replied 3 months ago

Is the indicator group working correctly?

Do all lights self-test at key on?

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Customer reply replied 3 months ago
Harness looks ok with visual, issue is circuit (d+) does not dis connect with key switch, remaining at battery voltage -1 volt until relay 1 or battery is disconnected
Mechanic: catmastertech, Technician replied 3 months ago

D+ wire is a yellow wire marked C444 correct?

This is the feed to the indicator group in the upper right console. I have replaced a few of these but, they had failed. I haven't replaced one specifically due to battery issues though.

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Customer reply replied 3 months ago
Indicator group appears ok-hour meter display is always on???
All functions appear n ormal
Yellow wire is C444E26 from splice with C444E27 (from resistor )
Mechanic: catmastertech, Technician replied 3 months ago

Yes, hour meter will stay on as long as the battery is connected. This is normal.

C444 does tie to a resistor and a diode in the D+ circuit.

I assume you have a schematic and can test the complete circuit?

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Customer reply replied 3 months ago
Done, all components wired correctly and test ok (diodes ok, resistance within tolerance
Mechanic: catmastertech, Technician replied 3 months ago

The main relay A connects to the fuse panel with the shutoff solenoid relay. Have you tried removing that relay and/or testing the shutoff solenoid for a current draw?

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Customer reply replied 3 months ago
Don't know where those relay and solenoids are? Fuse panel? Fuel shut off?
EC3?
Mechanic: catmastertech, Technician replied 3 months ago

Look for fuse F18 and relay 1. It should be the panel with the black connectors as the other fuse and relay panels have different colored connectors.

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Mechanic: catmastertech, Technician replied 3 months ago

See attached image

Fuses and Relays

  • Fuses

     

  • (2) Finger Trigger for the Work Tool

     

  • (3) Front Work Lights

     

  • (4) Rear Work Lights

     

  • (5) Left Tail Lamp

     

  • (6) Right Tail Lamp

     

  • (7) Spare

     

  • (8) Backup Alarm

     

  • (9) Cold Start

     

  • (10) Radio

     

  • (11) Spare

     

  • (12) Spare

     

  • (13) 12 volt power socket

     

  • (14) Hydraulic Quick Coupler

     

  • (15) Wiper

     

  • (16) Auxiliary Hydraulic ECM

     

  • (17) HVAC Blower Fan and the Solenoid for the Compressor

     

  • (18) Fuel Shutoff solenoid

     

  • (19) Interlock ECM

     

  • (20) Beacon

     

  • (21) Gauges

     

  • (22) The fan for the air conditioner condenser

     

  • (23) Ignition Switch

     

  • (24) Miscellaneous Power

     

  • (25) Horn

     

  • (27) Auxiliary Hydraulic C-

     

  • (28) Auxiliary Hydraulic C+

     

  • (29) Auxiliary Tools

     

  • (30) Auxiliary Electrical Control C1

     

  • (33) Spare

     

  • (34) Auxiliary Electrical Control C2

     

  • Relays

     

  • (1) Finger Trigger for the Work Tool

     

  • (26) Auxiliary Hydraulic C-Solenoid

     

  • (31) Auxiliary Electric Control C1

     

  • (32) Auxiliary Hydraulic C+Solenoid

     

  • (35) ECM signal for the Auxiliary Hydraulic C+ and the Auxiliary Hydraulic C-

     

  • (36) Auxiliary Electric Control C2

     

  • Diodes

     

  • (37) C-

     

  • (38) C+
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Customer reply replied 3 months ago
Thanks for the info, will need some time to check so things. Can I re'initiate this tomorrow?
Mechanic: catmastertech, Technician replied 3 months ago

Yes, I should be home most of the day. If not, I will reply as soon as possible.

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Customer reply replied 3 months ago
Ok, it's Easter Sunday. I'll be looking for eggs☺
Mechanic: catmastertech, Technician replied 3 months ago

Ok, good luck. Maybe you can catch that bunny too!

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Customer reply replied 3 months ago
Forget prior discussion re alternator, correct bench test analysis reveals matching results on machine. AM voltage of battery >9V. (Key not activated) Primary draw removed when fuse 24 (misc pwr) is removed, unable to determine from schematics what is connected to fuse 24.
Mechanic: catmastertech, Technician replied 3 months ago

That fuse is to the A pin of the ET connector,

the dome lamp and

the hour meter B+.

It also is to the connector for the MSS security connector.

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Mechanic: catmastertech, Technician replied 3 months ago

122 A82 RED wire

to 122 PA91 RED wire

to 122 C19 RED wire ties to Dome 122-C48 red wire

and hour meter 122-C49 B+

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Customer reply replied 3 months ago
Checking those circuits.
Mechanic: catmastertech, Technician replied 3 months ago

Ok, I will be here for the rest of the day

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Customer reply replied 3 months ago
With fuse reinstalled, battery voltage @ 12.3 (from 12.6) during testing (known good shop battery, not machine battery. Disconnect hour meter and dome light power leads and draw continues
Customer reply replied 3 months ago
Key switch must be activated (on position-no start) to reinitiate draw?
Mechanic: catmastertech, Technician replied 3 months ago

I would next look for the CONN 8 connector and check for a short on the wiring to the MSS connector.

This should be on the platform harness near the cab pivot area of the firewall. Near the center of the machine. LOC 34 on the schematic.

Also, inspect the ET connector for damage or moisture.

Yeah, I don't get how the key switch cycle must be activated to create the draw again. The only idea I have is a wire short in a harness that trips either the alternator or an ECM.

Did you try removing the fuel shutoff connection or its diode block?

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Customer reply replied 3 months ago
I did remove F18, didn't seem to affect drain?
Mechanic: catmastertech, Technician replied 3 months ago

After the key cycle, does any power remain on the other fuses, not on the battery circuits?

Have you checked the ECM's for power when the key is off? They have B+ markings but the circuit is still only on the KEY ON side of the fuses.

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Customer reply replied 3 months ago
Will have to reassemble upper cab controls ( again ) to inspect harness at pivot area. Thanks for your patience ☺
Mechanic: catmastertech, Technician replied 3 months ago

No problem, just keep me posted on your progress.

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Customer reply replied 3 months ago
I'll check the ecm power and advise.
Customer reply replied 3 months ago
Ever feel like you have been chasing your tail??? With 4 primary relays Disconnected and all major sub systems fuses out I still show 11V passing between DVM in series with ground at battery and negative cable.
Voltage disappears when B+ and D+ WIRES ARE diconnected from alternator key on and after. I'll have Mach owner order CAT oem and see what up. Have a good evening.
Mechanic: catmastertech, Technician replied 3 months ago

Yes, I do have those days too! It is crazy how often the "almost to spec" or "should be close enough" will drive us nuts!

That is why I don't have hair on my head anymore!

The alternator has been updated but it was years ago, like S/N 390 when they changed them out. Shouldn't be an issue unless the rebuild sheets are using old info and parts.

It did mention diodes but said the issue was "not charging" as the reason for the change.

Thanks for the update. Just let me know when you want to close this question.

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