PACCAR®

Q21-6159-1052 | Genuine Paccar® BMS-100 Battery Monitor System (Bergstrom)

NO CORE CHARGE

Free ground shipping
On eligible $100+ orders in the contiguous U.S. Shipping details

Product SKU: Q21-6159-1052
Availability: In Stock

Condition New

$1,399.00 - $1,399.00

$1,399.00

$1,399.00 - $1,399.00

$1,399.00

Hurry! only 1 left in stock!

Pickup available at 111 Belton Drive, Suite B. Usually ready in 24 hours

Ask about this product

Product details

Description	Battery Monitor System
Condition	New
Brand	Paccar®
Part Number	Q21-6159-1052

Fitment Guide

Peterbilt, Kenworth

The BMS-100 Battery Monitor System is an electronic controller used in heavy-duty trucks to monitor and manage both the starting batteries and auxiliary batteries. It's commonly found in PACCAR trucks (such as Kenworth and Peterbilt) equipped with battery-powered idle-reduction or sleeper HVAC systems.

Protects the starting batteries. It continuously monitors battery voltage and state of charge. If the batteries become too discharged, it disconnects non-essential loads so the truck still has enough power to start the engine.

Manages auxiliary batteries. Many trucks have a separate battery bank for sleeper accessories. The BMS-100 controls relays that connect or isolate the auxiliary batteries from the truck's charging system as needed.

Supports engine-off operation. Drivers can run equipment such as:
Sleeper air conditioning (ParkSmart/NITE systems)
Cabin heaters
Refrigerators
TVs
Inverters
Interior lighting
without unnecessarily draining the starting batteries.

Calculates battery health. It measures:
Starting battery voltage
Auxiliary battery voltage
Current flowing into and out of the batteries
Battery temperature
State of Charge (SoC)
State of Health (SoH)
Estimated remaining runtime for auxiliary loads.

Communicates with the truck. Using the SAE J1939 CAN bus, it reports battery status and diagnostic information to the truck's electronic control systems.

Signs of Faulty

1. Frequent dead batteries

Starting batteries discharge overnight.
Auxiliary batteries won't stay charged.
The truck needs frequent jump-starts despite good batteries.

2. Sleeper accessories stop working

The BMS may prematurely disconnect loads such as:

Sleeper HVAC (ParkSmart/NITE)
Refrigerator
Inverter
Interior lights
Power outlets

Sometimes these accessories shut off even when the batteries are well charged.

3. Incorrect battery readings

The truck may display:

Low battery warnings when batteries test good.
Battery percentage that changes unexpectedly.
Incorrect estimated runtime for auxiliary power.

4. Charging system issues

The BMS may fail to properly manage battery charging, causing:

Auxiliary batteries not charging while driving.
Starting batteries charging normally but auxiliary batteries remaining low.
Charging system warning messages.

5. CAN bus communication faults

Since the BMS communicates over the SAE J1939 CAN bus, a failure may trigger:

Communication fault codes.
Loss of battery status information.
Intermittent warning lights or messages.

6. Battery isolation problems

The battery isolation relay may:

Stay open when it should close, preventing charging.
Stay closed when it should open, allowing auxiliary loads to drain the starting batteries.

7. Intermittent electrical behavior

Symptoms may come and go, especially after:

Rain or high humidity.
Driving over rough roads.
Changes in temperature.

About the manufacturer

Headquartered in Bellevue, WA, PACCAR® is a Fortune 500 company specializing in heavy duty commercial vehicles. Founded in 1915 as the Pacific Car and Railway Company, PACCAR Inc grew from a small railway equipment supplier to one of the world's largest manufacturers of light, medium, and heavy duty trucks. It is a major designer and manufacturer of diesel engines and powertrain components through dealer networks in over 2,200 locations around the world. The company also operates parts distribution centers for aftermarket support that includes customer call centers operating 24 hours a day and state-of-the-art inventory management systems that speed up order processing.