Pinpoint Test Al: Abs (Anti-Lock Brake System) Module DTC (Diagnostic Trouble Code) C1A99 - Pressure Sensor

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Refer to Horn/Cigar Lighter for schematic and connector information.

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.

DTC Fault Trigger Conditions

DTC	Description	Fault Trigger Condition
ABS C1A99:28	Pressure Sensor: Signal Bias Level Out Of Range/Zero Adjustment Failure	Sets when the ABS module detects master cylinder pressure sensor within the HCU has failed.

Possible Sources

Incorrectly installed stoplamp switch
Brake drag (base brake system concern)
Wiring, terminals or connectors
HCU

AL1 CHECK FOR ABS (ANTI-LOCK BRAKE SYSTEM) MODULE DTC (DIAGNOSTIC TROUBLE CODE) C1A99

Ignition ON.

Clear the ABS DTCs.

Test drive the vehicle at speeds above 20 km/h (12 mph) and perform at least 2 regular stops.

Ignition OFF.

Ignition ON.

Carry out the ABS self-test.

Is DTC C1A99:xx currently present and active in the ABS module?

Yes

GO to AL2

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.

AL2 CHECK THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE HYDRAULIC PRESSURE PID (PARAMETER IDENTIFICATION)

NOTE: 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.
- Using a diagnostic scan tool,
  Access the ABS and monitor the BRKHYDPRESS (Bar) 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 GO to AL4

No GO to AL3

AL3 CHECK FOR BRAKE DRAG
- With the transmission in NEUTRAL, position the vehicle on a hoist. REFER to: Noise, Vibration and Harshness (NVH) .
- 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 GO to AL4

No DIAGNOSE and REPAIR the brake drag concern. REFER to: Brake System .

AL4 CHECK THE PCM (POWERTRAIN CONTROL MODULE) BOO1 AND BOO2 PID (PARAMETER IDENTIFICATION) S

Ignition ON.

Monitor the following PIDs while pressing and releasing the brake pedal.

Using a diagnostic scan tool,
Access the PCM and monitor the BOO1PID

Using a diagnostic scan tool,
Access the PCM and monitor the BOO2PID

Do the PIDs indicate ON with the brake pedal applied and OFF with the brake pedal released?

Yes

INSTALL a new HCU. 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 HCU and ABS module assembly. REFER to: Hydraulic Control Unit (HCU)
If this is a Ford paid repair, INCLUDE the RVC on the warranty claim form.

No	INSTALL a new BOO switch. REFER to: Stoplamp Switch When installing the new switch, USE the appropriate flex probe to VERIFY correct pin fitment at the connector.