Code No.79: Pressure switch system (open circuit or short
circuit)
OPERATION
- The pressure switch (for low-pressure warning) monitors brake fluid
pressure inside of the hydraulic brake booster (HBB). When the brake fluid
pressure decreases abnormally, the pressure switch (for low-pressure
warning) is turned off and the brake fluid low-pressure warning signal is
sent to the ABS-ECU.
- The pressure switch (for pump motor control) monitors brake fluid
pressure inside of the hydraulic brake booster (HBB). When the brake fluid
pressure decreases lower than the specified value, the pressure switch (for
pump motor control) is turned off and outputs the pump motor drive signal to
the ABS-ECU.
- The ABS-ECU monitors an open circuit of the pressure switch (for pump
motor control) (at 43 terminal).
- The ABS-ECU monitors an open circuit or short circuit of the pressure
switch (for low-pressure warning) (at 17 terminal).
DIAGNOSIS CODE SET CONDITIONS
The diagnosis code is set if the
pressure switch circuit is open or short, the ABS-ECU internal circuit
malfunction occurs or the hydraulic brake booster (HBB) pressure switch, or
master cylinder and hydraulic unit assembly malfunction occurs.
PROBABLE CAUSES
- Damaged wiring harness or connector
- Malfunction of the ABS-ECU
- Malfunction of the master cylinder and hydraulic unit assembly
[Integrated with the hydraulic brake booster (HBB)]
- Malfunction of the pressure switch [Integrated with the hydraulic
brake booster (HBB)]
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STEP 1. Check HBB connector B-107 and B-108 for loose, corroded or
damaged terminals, or terminals pushed back in the
connector.
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Q.
Is the check result normal?
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 Go to Step 2.
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 Repair the faulty connector or
terminal. Then go to Step 8.
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STEP 2. Check the pressure switch (for pump motor control) circuit
inside the HBB.
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(1)Depress the pedal repeatedly more than 40 times until the
pedal depressing force feels heavy with the ignition switch at the "LOCK"
(OFF) position to release the pressure of HBB power supply system.
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(2)Disconnect HBB connector B-108.
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(3)Measure the resistance between the terminals 33 and 35 at
the HBB.
OK: Approx. 1 kΩ
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(4)With the HBB connector B-108 disconnected, turn ON the
ignition switch to operate the pump motor.
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(5)During the pump motor operation, measure the resistance
value (resistance value at high accumulator pressure) between the HBB-side
connector terminal No. 33 and No. 35.
OK: 0
Ω
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Q.
Is the check result normal?
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Go to Step 3.
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Replace the master cylinder and
hydraulic unit assembly (Refer to  ). Then go to Step 8.
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STEP 3. Check the pressure switch (for low-pressure warning) circuit
inside the HBB.
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(1)Depress the pedal repeatedly more than 40 times until the
pedal depressing force feels heavy with the ignition switch at the "LOCK"
(OFF) position to release the pressure of HBB power supply system.
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(2)Disconnect HBB connector B-107.
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(3)Measure the resistance between the terminals 1 and 5 at
the HBB.
OK: Approx. 5.7 kΩ
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(4)Turn ON the ignition switch to operate the pump motor, and
then check that the pump motor stops.
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(5)Measure the resistance value (resistance value at high
accumulator pressure) between the HBB-side terminal No. 1 and terminal No.
5.
OK: Approx. 1 kΩ
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Q.
Is the check result normal?
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Go to Step 4.
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Replace the master cylinder and
hydraulic unit assembly (Refer to ). Then go to Step 8.
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STEP 4. Check the following harness wires.
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- The wire between HBB connector B-107 (terminal 1) and body
earth
- The wire between HBB connector B-108 (terminal 33) and body
earth
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Q.
Is the check result normal?
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Go to Step 5.
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Repair or replace it. Then go to
Step 8.
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STEP 5. Check ABS-ECU connector D-250 and D-251 for loose, corroded or
damaged terminals, or terminals pushed back in the
connector.
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Q.
Is the check result normal?
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Go to Step 6.
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Repair the faulty connector or
terminal. Then go to Step 8.
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STEP 6. Check the following harness wires.
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- The wire between HBB connector B-107 (terminal 5) and ABS-ECU
connector D-251 (terminal 17)
- The wire between HBB connector B-108 (terminal 35) and ABS-ECU
connector D-250 (terminal 43)
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Q.
Is the check result normal?
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Go to Step 7.
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Repair or replace it. Then go to
Step 8.
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STEP 7. Recheck for diagnosis code.
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(1)Erase the diagnosis code.
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(2)Recheck for diagnosis code.
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Replace the ABS-ECU (Refer to
GROUP 35B, ABS Control Unit ). Then go to Step 8.
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It can
be assumed that this malfunction is intermittent. Refer to GROUP 00, How to
Use Troubleshooting/Inspection Service Points - How to Cope
with Intermittent Malfunction .
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STEP 8. Recheck for diagnosis code.
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(1)Erase the diagnosis code.
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(2)Recheck for diagnosis code.
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Start over at Step 1.
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The
procedure is complete.
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