NHTSA ID Number: 11023469
Manufacturer Communication Number: CBR 2495 092025
TSB/Document Date: 2025-10-01
Summary
The purpose of the 48V EATS heater system is to provide additional heat to the exhaust stream allowing the EATS to become active earlier during acold start and during engine operation that produces low exhaust gas temperatures.
9/30/25, 10:03 AM
Article
Preview Solution CBR-2495-2
Carb 24 Phase 1 - 48V Diagnostics Guide
Published 4 September 2025
Valid for
Volvo
Chassis - VNL and VNR
Mack Chassis - AN and GR
Model Year - 2023 to 2024 (CARB 2024 only)
Overview
The purpose of the 48V EATS heater system is to provide additional heat
to the exhaust stream allowing the EATS to become active earlier during a
cold start and during engine operation that produces low exhaust gas
temperatures. The key components of the 48V heater system are the:
Electric Machine (48V Alternator)
48V Lithium Ion Battery
EHCM (Eaton Heater Control Module
Heater element in the EATS assembly
The Electric Machine, battery and EHCM are wired in parallel. Nominal
48V is only present with the ignition ON with certain fault codes not being
present. Many 48V faults will NOT turn ON the 48V system and no 48V
will be measured at any of the above components.
The 48V battery will NOT have 48V present at the battery posts with the
engine OFF and Ignition key OFF. Checking voltage with ignition key
OFF does not indicate a dead battery.
More detailed information on the operation of the 48V heater system can
be found in impact under Description, Design and Function:
Function Group 25: For information on EATS heater system
Function Group 31: For information on 48V Battery
; Live UI
https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/8ArYedXAbJ8Ah7TyziTZDNcbINKlj7CXNfiib1A0TL8*/!TABTHREAD1?pyActivity…
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Function Group 321: For information on 48V Electric Machine
(alternator)
Diagnostics
The first step when diagnosing ANY 48V system faults starts by observing
the LED push button/light located on top of the 48V battery located in the
CARB box on the frame rail of the truck. The aluminum CARB box cover
must be removed to view the battery LED.
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1. Press and release the SOC LED on top of the 48V battery with engine
off, key OFF. Should blink a quick red then a white light, indicating the
battery has sufficient charge for operation. If no light comes ON, battery is
discharged and needs to be replaced. (Except when P3515/87 is active)
2. With Key On, Engine OFF LED should blink green three times,
indicating a successful pre-charge and will allow the contacts inside the
battery to close with nominal 48V indicated at all heater system
components. If the LED blinks red it indicates an unsuccessful pre charge
and the contacts will NOT close inside the battery and nominal 48V will
NOT be indicated on any of the heater system components.
If LED blinks red, turn ignition OFF and disconnect positive cable at
48V battery post.
With Key On, Engine OFF LED should blink green. If it continues to
blink red, the battery has an internal fault. Replace battery and
retest for blinking green LED
Common DTCs for 48V system.
If all three DTCs listed below are set:
P028A14 - Charge Air Cooler Cooling Fan Control (Circuit
short to ground or open)
P2F8916 - Catalyst Heater Control Module "A" Voltage
Sensor Circuit (Circuit voltage below threshold)
P351787 - Motor/Generator (Missing message)
Check fuse FE7 (CARB24 FAN) to see if it is missing or open. This
fuse is located in fuse box under the hood.
If P351587 (missing battery message) is active:
Check CAN cable pigtail from battery to CARB box
wiring harness connections and/or for damaged wires.
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P/N 24583917
If P350B63 - (Intermediate Voltage Battery Precharge Circuit,
Circuit/Component Protection Time-Out) is active:
Check positive cable from CARB box fuse block to 48V
Generator for rubbing/short to battery hold down bracket.
Reinsulate cable and reposition cable away from the
bracket hold down.
If no rubbing or shorts are found, check 48V cables for
shorts to ground from CARB box to under hood routing
and to EATS heater.
; Live UI
If no shorts are found, check for the swapped location of
long 48V cables. Long cables run from CARB box to 48V
alternator (teal) and from EHCM to heater (yellow). Cable
pairs are almost identical in length. Correct routing and
retest for DTC removal.
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P351162 - (Intermediate Voltage Battery Pack Voltage, Signal
Compare Failure) is active:
Clear DTC and rescan faults. If DTC is active again,
contact tech support for further direction.
P2F8D85 - (Catalyst Heater Control Module "A" Temperature Sensor
Circuit, Signal Above Allowable Range) and/or P351822 (Intermediate Voltage Electrical System, Signal Amplitude Greater
Than Maximum), sets “Get Out of Truck” message on instrument
cluster are active:
This is a known issue that will be addressed at a later
date.
P35172F, P351709, and P351738: Do not diagnose these codes at
this time.
; Live UI
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TSB/Document ID: CBR 2495 092025
Replacement Service Bulletin Number:
MFR Communication Date: 2025-09-04
MFR Internal Campaign ID/Software Version:
Communication Type: Service Bulletin/Repair Instructions
NHTSA Components: ENGINE
MFR Component System:
MFR Component Subsystem:
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