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Pinpoint Tests CT: ABS Module DTC C1A99 - Pressure Sensor
Normal Operation And Fault Conditions
The ABS module uses a pressure sensor located inside the HCU to monitor the integrity of the
hydraulic system. When the brake pedal is pressed, the ABS module compares the value of the
brake fluid line pressure sensor to the BOO switch input from the PCM over the HS-CAN. If the
brake fluid pressure sensor value is not comparable to the BOO switch input, the ABS module
sets one or more DTCs.
PPT CT ABS MODULE DTC FAULT TRIGGER CONDITIONS
DTC Description Fault Trigger Conditions
C1A99:01
Pressure Sensor: General Electrical
Failure
This DTC indicates the brake fluid line hydraulic
pressure sensor signal circuit located inside the HCU
has failed.
C1A99:28
Pressure Sensor: Signal Bias Level
Out of Range/Zero Adjustment
Failure
This DTC indicates the brake fluid line hydraulic
pressure sensor located inside the HCU has failed.
Possible Causes
Incorrectly installed stoplamp switch
Brake drag (base brake system concern)
Wiring, terminals or connectors
HCU
CT1: RECHECK FOR ABS MODULE DTC C1A99
Ignition ON, engine OFF.
Carry out the ABS self-test.
Is DTC C1A99:xx currently present and active in the ABS module?
Yes No
Go to
CT2.
GATHER information from the customer about conditions necessary to duplicate the
concern.
Some things to ask the customer may include; how often, drive time, down time, climate
conditions (inside and outside the vehicle), speed traveling or maneuvering performed
when the fault occurs.
OPERATE the vehicle in the conditions outlined by the customer and MONITOR the
PCM BOO1 and BOO2 PIDs, and the ABS module Hydraulic pressure PIDs to
determine a focus area.
If there is pressure above 1, 379 kPa (200 PSI) and no BOO reading, an incorrectly
installed stoplamp switch is the most likely cause.
YMMS: Apr 11, 2021
Engine: 2.3L Eng License:
VIN: Odometer:
2020 Ford Ranger Lariat
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CT2: CHECK THE ABS MODULE HYDRAULIC PRESSURE PID
NOTE: The brake pressure PID should read close to 0 kPa
(0 PSI) with the brake pedal released and increase when
applying the brake pedal.
Access the ABS and monitor the BRKHYDPRESS (PRESS) PID.
While monitoring the PID, fully apply the brake pedal.
Does the PID read close to 0 kPa (0 PSI) without the brake pedal applied and increase
when the pedal is pressed?
Yes No
Go to CT4. Go to CT3.
CT3: CHECK FOR BRAKE DRAG
With the transmission in NEUTRAL, position the vehicle on a hoist. Refer to the Jacking and
Lifting article.
Spin each wheel by hand and check for any indication of brake drag.
Do all 4 wheels spin freely with little to no resistance?
Yes No
Go to CT4.
DIAGNOSE and REPAIR the brake drag concern.
REFER to the Brake System General Information article.
CT4: CHECK THE PCM BOO1 AND BOO2 PIDS
Ignition ON, engine OFF.
Monitor the following PIDs while pressing and releasing the brake pedal.
Access the PCM and monitor the BOO1 (MODE) PID.
Access the PCM and monitor the BOO2 (MODE) PID.
Do the PIDs indicate ON with the brake pedal applied and OFF with the brake pedal
released?
Yes No
INSTALL a new EBB assembly.
CHECK OASIS for any service articles: TSB,
GSB, SSM or FSA.
If a service article exists for this concern,
DISCONTINUE this test and FOLLOW the
service article instructions.
If no service articles address this concern,
INSTALL a new EBB unit (HCU and ABS
module assembly).
If this is a Ford paid repair, INCLUDE the RVC
on the warranty claim form.
INSTALL a new BOO switch.
REFER to the Exterior Lighting article.
When installing the new switch, USE the
appropriate flex probe to VERIFY correct pin
fitment at the connector.
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