Traction Control Switch Removal; Installation; Hcu - Hydraulic Control Unit Description - Hydraulic Control Unit (Hcu) - Chrysler PT Cruiser Service & Repair Manual

PT
TONE WHEEL (Continued)
If wheel speed sensor to tone wheel contact is evi-
dent, determine the cause and correct it before
replacing the wheel speed sensor or tone wheel.
Check the gap between the speed sensor head and
the tone wheel to ensure it is within specifications.
For wheel speed sensor air gap specifications, (Refer
to 5 - BRAKES - ABS - SPECIFICATIONS).
Excessive tone wheel runout can cause erratic
wheel speed sensor signals. For tone wheel runout
specifications, (Refer to 5 - BRAKES - ABS - SPECI-
FICATIONS). If tone wheel runout is excessive,
determine if it is caused by a defect in the driveshaft
assembly or hub and bearing. Replace as necessary.
Tone wheels are pressed onto their mounting sur-
faces and should not rotate independently from the
mounting surface. Replace the front driveshaft or
rear hub and bearing as necessary.
TRACTION CONTROL SWITCH
REMOVAL
NOTE: The Traction Control Switch (Fig. 13) is
located within the accessory switch bezel on the
instrument panel.
Fig. 13 Traction Control Switch Location
1 - TRACTION CONTROL SWITCH
(1) Remove the accessory switch bezel and then
remove the traction control switch from it. (Refer to
23 - BODY/INSTRUMENT
SWITCH BEZEL - REMOVAL)

INSTALLATION

(1) Install the traction control switch in the acces-
sory switch bezel, then install the bezel on the
instrument panel. (Refer to 23 - BODY/INSTRU-
MENT PANEL/ACCESSORY SWITCH BEZEL -
INSTALLATION)
(2) Road test the vehicle to ensure proper opera-
tion of the switch and ABS.
HCU - HYDRAULIC CONTROL
UNIT
DESCRIPTION - HYDRAULIC CONTROL UNIT
(HCU)
The hydraulic control unit (HCU) is mounted to
the CAB as part of the ICU (Fig. 19). The HCU con-
trols the flow of brake fluid to the brakes using a
series of valves and accumulators. A pump/motor is
mounted on the HCU to supply build pressure to the
brakes during an ABS stop.
VALVES AND SOLENOIDS
The valve block contains four inlet valves and four
outlet solenoid valves. The inlet valves are spring-
loaded in the open position and the outlet valves are
spring-loaded in the closed position during normal
braking. The fluid is allowed to flow from the master
cylinder to the wheel brakes.
During an ABS stop, these valves cycle to maintain
the proper slip ratio for each wheel. The inlet valve
closes preventing further pressure increase and the
outlet valve opens to provide a path from the wheel
brake to the HCU accumulators and pump/motor.
This releases (decays) pressure from the wheel brake,
thus releasing the wheel from excessive slippage.
Once the wheel is no longer slipping, the outlet valve
is closed and the inlet valve is opened to reapply
(build) pressure.
If the ABS includes the traction control feature,
there are four other valves in the HCU. Two traction
control (TC) valves, mounted in the HCU valve block,
are normally in the open position and close only
when the traction control is applied. There are also
two shuttle valves which control pressure return to
the master cylinder under ABS and traction control
conditions.
BRAKES - ABS 5 - 83
PANEL/ACCESSORY