1999–2001 Isuzu NKR, NPR, NQR ABS Workshop Manual (P/N LGBRK-WE-0101)

• ISUZU NKR, NPR, and NQR ABS workshop manual: a 70-page PDF, Section 5A4, manual number LGBRK-WE-0101, first edition January 2001. Applicable to vehicles in markets outside the USA and Canada.
• Diagnostic documentation includes 17 DTC charts, ABS warning-light diagnosis, and symptom-based troubleshooting with and without the Tech 2 scan tool.
• Front and rear wheel speed sensor and rotor service covers removal, inspection, repair, and installation, with four wheel-specific output inspection procedures and a separate Tech 2 check.
• EHCU removal and installation is covered alongside hold-valve and release-valve tests for identifying incorrect brake-pipe or valve-harness connections after repair.
• Electrical fault tracing is supported by system wiring diagrams, EHCU connector pin-out checks, connector views, and component-location drawings.

Component and System Documentation

This N-series manual documents the four-wheel Anti-lock Brake System (ABS). It explains how the Electronic Hydraulic Control Unit (EHCU) combines the Electronic Brake Control Module (EBCM) and Hydraulic Unit (HU), with descriptions of the solenoid valves, plunger pump, motor, reservoir, and check valve.

The Tech 2 identification examples distinguish 2WD, 4WD, and ABS/ASR configurations. Repair coverage centers on ABS components, and the EHCU is replaced as an assembly, not internally overhauled. General mechanical brake diagnosis is referred to Section 5A; this publication is not a complete truck repair manual or a separate ASR service manual.

Tech 2 Diagnosis and Fault Isolation

Scan-tool coverage includes plotting snapshot graphs, interpreting data displays, and performing actuator tests for the return pump relay, solenoid valves, ABS relay, warning lamp, and exhaust brake cut relay. Snapshot recording and replay allow comparison of front-to-rear and side-to-side wheel speeds when tracking an intermittent complaint.

Current and history DTC information, code clearing, and the Clear & Reset Vehicle Type function are explained. Fault charts address vehicle-type errors, rear-sensor supply faults, EHCU voltage, motor circuits, solenoid circuits, individual wheel sensor faults, and tire-size errors. The manual identifies a specific diagnostic limitation: DTC 20, Reference Voltage High, is confirmed through warning-light flash diagnosis rather than Tech 2.

Symptom charts cover frequent ABS operation without adequate deceleration, uneven braking, wheel lockup, abnormal pedal feel, and hydraulic-unit noise when the brakes are not applied.

Specification and Inspection Data

This reference includes inspection parameters covering speed sensor output voltage, circuit resistance specifications, and tightening torques for braking components. Front coil-type sensors and rear Hall IC sensors have different test methods. Sensor fault isolation also addresses damaged rotor teeth, iron contamination, bearing play, and intermittent harness connections.

Rotor replacement procedures extend into hub removal and reassembly, bearing and oil-seal installation, and preload adjustment. Front hub data distinguish new and reused bearings; rear hub preload is covered separately. Rear sensor-bracket tightening specifications distinguish the 12,000- and 14,500-lb GVW models from the 17,950-lb model.

The front rotor procedure warns that an unsupported caliper can stretch or damage the brake hose. EHCU precautions address damage from electrostatic discharge and improper electrical probing.

Wiring Diagrams and Special Tools

The 12V and 24V electrical systems have separate circuit diagrams spanning four pages in total. The Connector List includes the J-500 EHCU connector, while the Part Location drawing identifies sensors, grounds, relays, fuses, and the diagnostic connector. Other useful references are the Basic Diagnostic Flow Chart and the Front Speed Sensor Rotor and Associated Parts exploded view.

Special-tool references identify connector test adapter kit 5-8840-0385-0 (J-35616) and high-impedance multimeter 5-8840-0285-0 (J-39200). The scan-tool setup also covers the Isuzu PCMCIA card, SAE 16/19 adapter, and DLC cable.

Working on hydraulic brake systems involves critical safety components. All service data shown here is for reference only, as qualified technicians and the original OEM documentation remain the authoritative source for any hands-on repair.