Isuzu Fault Codes
Isuzu builds the most common cab-over Class 4-7 delivery trucks in North America (NPR, NQR, FTR, FVR, FRR), powered by the 4HK1-TC and 6HK1 diesel engines. The 4HK1 in particular has been the dominant engine in city delivery, parcel, and light-vocational work since 2005. Isuzu fault codes are read with the Isuzu IDSS (Isuzu Diagnostic Service System) scan tool and follow standard P-code + manufacturer-specific DTC conventions.
88 fault codes documented· 4 engine variants · P-codes + Isuzu DTCs (IDSS) · 2003 - present
Most Common Isuzu Fault Codes
Showing 24 of 88 Isuzu codes, sorted by severity. Each links to causes, diagnostics, common fixes, and repair cost estimates.
ISUZU-C1025 serious
ABS Hydraulic Control Unit Valve Relay
ISUZU-C1035 serious
ABS Solenoid Valve Circuit - Front Left
ISUZU-P0087 serious
Fuel Rail / System Pressure Too Low
ISUZU-P0088 serious
Fuel Rail / System Pressure Too High
ISUZU-P0089 serious
Fuel Pressure Regulator Performance
ISUZU-P0093 serious
Fuel System Leak Detected - Large Leak
ISUZU-P0191 serious
Fuel Rail Pressure Sensor Range/Performance
ISUZU-P0192 serious
Fuel Rail Pressure Sensor Circuit Low
ISUZU-P0193 serious
Fuel Rail Pressure Sensor Circuit High
ISUZU-P0234 serious
Turbocharger Overboost
ISUZU-P0251 serious
Injection Pump Fuel Metering Control 'A' Malfunction
ISUZU-P0252 serious
Injection Pump Fuel Metering Control 'A' Range/Performance
ISUZU-P0299 serious
Turbocharger Underboost / Wastegate Range
ISUZU-P0335 serious
Crankshaft Position Sensor Circuit
ISUZU-P0340 serious
Camshaft Position Sensor Circuit
ISUZU-P0420 serious
Catalyst System Efficiency Below Threshold (DOC)
ISUZU-P042E serious
EGR Valve Stuck Open
ISUZU-P132B serious
Turbocharger Boost Control A Performance
ISUZU-P2002 serious
DPF Efficiency Below Threshold Bank 1
ISUZU-P2003 serious
DPF Efficiency Below Threshold Bank 2
ISUZU-P203F serious
Reductant Level Low
ISUZU-P2047 serious
Reductant Injector Circuit Open
ISUZU-P2048 serious
Reductant Injector Circuit Low
ISUZU-P2049 serious
Reductant Injector Circuit High
Isuzu Engine Versions
| Engine | Years | Applications | Notes |
|---|---|---|---|
| Isuzu 4HK1-TC | 2005-present | Isuzu NPR-HD, NPR-XD, NQR; Class 4-5 cab-over delivery | 5.2L I4 turbo. The most common Isuzu engine in North America. Single overhead cam, common-rail, EGR + DPF + SCR (2010+). |
| Isuzu 6HK1 | 2003-present | Isuzu FTR, FVR, FRR; Class 5-7 box truck and stake | 7.8L I6 turbo. Heavier counterpart to the 4HK1. Same emissions architecture and diagnostic approach. |
| Isuzu 4JJ1 | 2008-present | Isuzu D-Max pickup (international), some commercial | 3.0L I4. Common in light-commercial and pickup applications outside the US. |
| Isuzu 6WG1 / 6UZ1 | 2007-present | Heavy industrial / construction (excavators, wheel loaders) | Off-highway industrial 15.7L / 9.8L variants. Used by Hitachi, Doosan, JCB, Sumitomo and other equipment OEMs. |
Common Isuzu Issues
- DPF clogging from short-trip city delivery duty cycles -- forced regen via Isuzu IDSS scan tool
- DEF dosing unit and tank heater failures, especially in cold-weather operations
- EGR valve carbon-fouling and position sensor faults
- Common-rail pressure regulator (PCV) and SCV (suction control valve) failures
- Glow plug controller faults causing cold-start issues
- Turbo VGT actuator sticking -- requires actuator clean / replace
- Engine harness and sensor connector corrosion in coastal / road-salt environments