KC-2040

2/28/22, 12:19 PM
Article
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P21CA00 And Other Power Faults Leading To
Communication Faults And SCR Inducement
(Derate)
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Background
It is possible that a progressive loss of electrical power to the
Aftertreatment Control Module (ACM) will result in the ACM cutting power
to the Exhaust Aftertreatment System (EATS) sensors – NOx, Particulate
Matter (PM) and DEF Quality, Level and Temperature sensor. This
triggers communication faults for these sensors and ultimately puts the
system into SCR Inducement. The root cause is often related to loss of
power or battery voltage and/or grounding issues. The instruction below
describes the most likely causes and provides steps for troubleshooting.
Symptoms
• Presence of P21CA along with other ACM power and communication
faults P220A, P220B, P24D0, U029D, U029E, U02A2, U02A3, P0562.
• SCR inducement and/or derate.
P21CA00
Reductant Control Module Supply Voltage
P220A1C
NOx Sensor Supply Voltage Circuit (Bank 1 Sensor 1)
P220B1C
NOx Sensor Supply Voltage Circuit (Bank 1 Sensor 2)
P24D000
Particulate Matter Sensor Supply Voltage Circuit Low
U029D00
Lost Communication With NOx Sensor "A"
U029E00
Lost Communication With NOx Sensor "B"
U02A200
Lost Communication with Reductant Quality Module
U02A300
Lost Communication With PM Sensor
P056200
ECU Battery Potential Below Range
This pattern of codes indicates that there are issues with the ACM power
supply or ground connections. Typically, this combination develops over
time as a connection deteriorates. Eventually the effective voltage to the
ACM drops below 8V and there is insufficient power to support
the sensors controlled by the ACM - NOx, PM and DEF
UI
; Live
level/temp sensors. Communication is lost to these devices.
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Once sensor communication codes (U029D, U029E, U02A2) are
triggered, the truck will go into SCR Inducement followed by derate.
Diagnosis And Repair
IMPORTANT
Presence of any combinations of P24D0, P21CA, P0562, generally
does NOT indicate the ACM is 'bad' or a PM sensor is 'bad'.
Required Tools
Part Number
9998699
9990014
88890074 (or equivalent)
Description
Break-Out Box
62-Pin ACM Connector Harness
Multimeter
Quantity
1
1
1
Initial Checks
This combination of faults is frequently caused by a loose or
faulty connection on battery power or ground (but not fully disconnected if fully disconnected, DTCs U116F and U010E would also be present).
• Check that ALL the ACM power and ground connections are
securely tightened.
- Ensure battery nuts are tightened to 15 lb-ft (20 Nm). If nuts are
loose, replace nuts with PN 25153442. Positive connections will
also require red protective boot PN 20831182.
- Ensure multiple ring terminals on a common stud are fanned out
and lying flat against each other.
- Ensure ring terminals and other contact points are clean and free
from any terminal protectant coating or wax.
• If there is no evidence of loose battery connections: Continue to
the checks below.
Other items to check
; Live UI
1. Check the battery condition as follows:
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1.1. Check the complete battery pack voltage.
1.1.1. Start the truck.
1.1.2. Run the engine at fast idle (1000 RPM) for 1 minute.
1.1.3. Turn the truck off, then return the key to the ON
position.
1.1.4. Check voltage with all of the batteries still connected
to one another.
• All battery positive terminals are connected together
by busbars or cables, and all battery negative
terminals are connected together.
1.1.5. Make a note of the voltage and evaluate results:
• For a fully charged system, in good condition,
the voltage should be 12.4 - 12.6V for standard
flooded lead-acid batteries, or 12.6 - 12.8V for
AGM-type batteries.
• Low battery voltage is indicative of an inadequate
charging system
- Potential causes include corroded cables, dirty
connections and/or weak or defective batteries.
1.2. Check individual battery condition.
1.2.1. Disconnect the busbars and cables.
1.2.2. Inspect and clean all interconnecting terminals.
Ensure there is no corrosion.
1.2.3. Check each battery voltage and perform a load test
on each battery individually.
1.2.4. Evaluate results:
• If one battery's voltage is significantly lower than
the others, or lower than the measurement from
Step 1.1.5, OR fails a load test: The battery may be
; Live UI
bad or there may be a connection issue such as
i
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excessive corrosion on the busbar or terminal,
inhibiting proper charging.
1.2.5. Replace or clean any corroded part as needed.
1.2.6. Reconnect the busbars and/or cables.
1.3. Check the battery pack voltage while charging system is
active.
1.3.1. Start the truck.
1.3.2. Run the engine at fast idle (1000 RPM) for 1 minute.
1.3.3. With the engine still running, recheck battery voltage:
• Voltage should rise to 13.5-14.5V rapidly.
• If the voltage is less than 13V: Run then engine for
an additional minute and recheck, as the batteries may
have been deeply discharged.
1.3.4. Evaluate results:
• If the voltage remains less than 13V: There is an
issue with the alternator or the alternator belt.
• If the alternator belt is in good condition, there is an
issue with the alternator.
If there are no issues found from the checks above or the code(s)
continue to log after the steps above are followed, normal
diagnostic steps should be followed in Premium Tech Tool.
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Tags
p21ca00
p220a1c
p220b1c
p24d000
u029d00
u029e00
u02a200
u02a300
p056200
; Live UI
p21ca-00
p220a-1c
p0562 00
acm power
eats datalink
u02a3-00
p220b 1c
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p0562-00
acm power
p24d0-00
u029d-00
eats datalink
u029e-00
Related links and attachments
FSB 284-069
Article
p220b-1c
u02a2-00
Feedback
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