Infiniti QX56 (JA60). Manual - part 425

EC-352

< COMPONENT DIAGNOSIS >

[VK56DE]

P1574 ASCD VEHICLE SPEED SENSOR

OK or NG

OK

>> GO TO 3.

NG

>> Repair or replace.

3.

CHECK COMBINATION METER FUNCTION

Check combination meter function.

Refer to 

MWI-5

.

>> INSPECTION END

P1805 BRAKE SWITCH

EC-353

< COMPONENT DIAGNOSIS >

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P1805 BRAKE SWITCH

Description

INFOID:0000000005149417

Brake switch signal is applied to the ECM through the stop lamp switch when the brake pedal is depressed.

This signal is used mainly to decrease the engine speed when the vehicle is driving.

On Board Diagnosis Logic

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The MIL will not light up for this self-diagnosis.

FAIL-SAFE MODE

When the malfunction is detected, the ECM enters fail-safe mode.

DTC Confirmation Procedure

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1. Turn ignition switch ON.
2. Fully depress the brake pedal for at least 5 seconds.
3. Erase the DTC with CONSULT-III.
4. Check 1st trip DTC.
5. If 1st trip DTC is detected, go to 

EC-353, "Diagnosis Procedure"

.

Diagnosis Procedure

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1.

CHECK OVERALL FUNCTION-II

 With CONSULT-III

Check “BRAKE SW2” indication in “DATA MONITOR” mode. 

 Without CONSULT-III

DTC No.

Trouble diagnosis name

DTC detecting condition

Possible cause

P1805
1805

Brake switch

A brake switch signal is not sent to ECM for ex-
tremely long time while the vehicle is driving.

• Harness or connectors

(Stop lamp switch circuit is open or short-
ed.)

• Stop lamp switch

Engine operating condition in fail-safe mode

ECM controls the electric throttle control actuator by regulating the throttle opening to a small range.
Therefore, acceleration will be poor.

Vehicle condition

Driving condition

When engine is idling

Normal

When accelerating

Poor acceleration

CONDITION

INDICATION

Brake pedal: Fully released

OFF

Brake pedal: Slightly depressed

ON

EC-354

< COMPONENT DIAGNOSIS >

[VK56DE]

P1805 BRAKE SWITCH

Check voltage between ECM terminal 101 and ground under the fol-

lowing conditions.

OK or NG

OK

>> GO TO 6.

NG

>> GO TO 2.

2.

CHECK STOP LAMP SWITCH POWER SUPPLY CIRCUIT 

1. Disconnect stop lamp switch harness connector.

2. Check voltage between stop lamp switch terminal 3 and ground

with CONSULT-III or tester.

OK or NG

OK

>> GO TO 4.

NG

>> GO TO 3.

3.

DETECT MALFUNCTIONING PART

Check the following.

• Harness connectors M31, E152

• Fuse block (J/B) connector M60

• 10 A fuse (No. 20)

• Harness for open and short between stop lamp switch and battery

>> Repair open circuit or short to ground or short to power in harness or connectors.

4.

CHECK STOP LAMP SWITCH INPUT SIGNAL CIRCUIT FOR OPEN AND SHORT

1. Turn ignition switch OFF.

2. Disconnect ECM harness connector.

3. Check harness continuity between ECM terminal 101 and stop lamp switch terminal 4.

Refer to Wiring Diagram.

4. Also check harness for short to ground and short to power.

CONDITION

VOLTAGE

Brake pedal: Fully released

Approximately 0 V

Brake pedal: Slightly depressed

Battery voltage

PBIB1537E

BBIA0373E

Voltage: Battery voltage

PBIB2102E

Continuity should exist.

P1805 BRAKE SWITCH

EC-355

< COMPONENT DIAGNOSIS >

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OK or NG

OK

>> GO TO 5.

NG

>> Repair open circuit or short to ground or short to power in harness or connectors.

5.

CHECK STOP LAMP SWITCH 

Refer to 

EC-355, "Component Inspection"

.

OK or NG

OK

>> GO TO 6.

NG

>> Replace stop lamp switch.

6.

CHECK INTERMITTENT INCIDENT

Refer to 

GI-35, "How to Check Terminal"

 and 

GI-38, "Intermittent Incident"

.

>> INSPECTION END

Component Inspection

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STOP LAMP SWITCH

1. Disconnect stop lamp switch harness connector.

2. Check continuity between stop lamp switch terminals 3 and 4

under the following conditions.

3. If NG, adjust stop lamp switch installation, refer to 

BR-15,

"Inspection and Adjustment"

, and perform step 2 again.

BBIA0373E

Conditions

Continuity

Brake pedal: Fully released

Should not exist.

Brake pedal: Slightly depressed

Should exist.

PBIB2103E