# DERATE — Truck Fault Codes

> Diagnóstico de códigos de falla para camiones diésel. El operador toma una foto del tablero o de la pantalla del escáner (o escribe el código) y recibe: severidad, qué significa, causa más probable, pruebas en orden y una orden de trabajo en PDF para el taller. Bilingüe español / inglés, con lectura en voz alta.

> Diesel truck fault-code diagnosis. A driver photographs the dash cluster or the mechanic's scanner screen (or types the code) and gets severity, meaning, most likely cause, tests in order, and a shareable PDF work order. Spanish / English with text-to-speech.

Publisher: VARGER GROUP LLC
Site: https://derate.app/
Supported code formats: J1939 SPN/FMI, OBD-II (Pxxxx), OEM dash telltales.
Supported platforms: Cummins, Paccar MX, Detroit Diesel, Volvo, Mack, International, Freightliner, Kenworth, Peterbilt.
Severity semantics: RED octagon = stop now, AMBER triangle = caution / possible derate, WHITE-GREEN circle = information only.

## Key pages

- [Diagnóstico (home)](https://derate.app/): capture a dash or scanner photo, or enter SPN/FMI manually.
- [Cómo leer códigos sin escáner](https://derate.app/guide): 5-step guide from photo to work order.
- [Biblioteca de códigos (ES)](https://derate.app/codigos): free index of fault codes in Spanish.
- [Fault code library (EN)](https://derate.app/codes): free index of fault codes in English.
- [Planes y precios](https://derate.app/pricing): single rescue diagnosis, driver plan, technician plan.
- [Privacidad](https://derate.app/privacy) · [Términos](https://derate.app/terms)

## MCP Server

DERATE exposes a public Model Context Protocol (MCP) server so AI assistants and agents can query the fault-code library directly. No authentication, read-only.

- Endpoint: https://derate.app/mcp (Streamable HTTP, JSON-RPC 2.0 over POST)
- Descriptor: https://derate.app/.well-known/mcp.json

- `get_truck_fault_code`: Look up a diesel truck fault code (J1939 SPN/FMI such as 'SPN 3251 FMI 0', or an OBD-II code such as 'P2002') in DERATE's public fault-code library. Returns what the code means, its severity, whether it is safe to keep driving, probable causes, the recommended tests, and the canonical URL of the public page for that code. Works without any account.
- `interpret_derate`: Explain a diesel truck engine derate or power-loss symptom described in plain language (for example 'DEF light on and truck limited to 55 mph'). Returns the most likely cause, how urgent it is, the immediate action to take, and matching public fault-code pages. This is the free public interpretation; the full guided diagnosis with tests and a work order runs in the DERATE app.
- `search_fault_code_library`: Full-text search over DERATE's public diesel truck fault-code library by code, system, dashboard light or symptom words. Returns a list of matching entries with code, title, severity, system and the canonical public URL.
- `list_supported_engine_families`: List the diesel truck engine families and code protocols DERATE interprets (J1939 SPN/FMI and OBD-II), so an agent knows whether a given truck is covered before looking up a code.

The same tools are also registered in-page via WebMCP (navigator.modelContext) for browser agents.

## Commerce

Public product feed of DERATE's plans, generated from the same price catalog the pricing page uses. Status of agentic checkout (ACP): not enabled yet.

- Product feed (JSON): https://derate.app/feed/products.json
- Product feed (CSV): https://derate.app/feed/products.csv
- Commerce descriptor: https://derate.app/.well-known/agent-commerce.json
- Pricing page: https://derate.app/pricing
- ACP create session (POST): https://derate.app/api/acp/checkout_sessions
- ACP update session (POST): https://derate.app/api/acp/checkout_sessions/{id}
- ACP complete session (POST): https://derate.app/api/acp/checkout_sessions/{id}/complete
- ACP cancel session (POST): https://derate.app/api/acp/checkout_sessions/{id}/cancel

While ACP is disabled every endpoint answers HTTP 503 with { "error": "acp_not_enabled" }. Humans can buy any plan on the pricing page.

## Frequently asked

- What is an engine derate? A power or speed reduction commanded by the engine ECM after a fault (commonly DEF/SCR, DPF, or aftertreatment) to protect the engine and force repair; it escalates in stages down to a 5 mph limp mode.
- Can DERATE read codes without an OBD scanner? Yes — it reads the codes from a photo of the instrument cluster or of a scanner screen; no hardware dongle is required.
- Does it replace a technician? No. It gives an objective diagnosis, an ordered test plan, and a work order; a qualified technician performs the repair.

## Fault codes (Spanish)

- [P0299 — Turbo con poca presión](https://derate.app/codigo/p0299): El turbo no da la presión que pide el motor. Severidad: YELLOW. Sistema: Admisión / Turbo.
- [SPN 102 FMI 18 — Presión del turbo](https://derate.app/codigo/spn-102-fmi-18): La presión del múltiple de admisión está baja: falta fuerza. Severidad: YELLOW. Sistema: Admisión / Turbo.
- [SPN 639 FMI 2 — Bus de datos](https://derate.app/codigo/spn-639-fmi-2): La red del camión pierde comunicación entre módulos. Severidad: YELLOW. Sistema: Eléctrico / J1939.
- [SPN 110 FMI 0 — Temperatura alta](https://derate.app/codigo/spn-110-fmi-0): El refrigerante está muy caliente: riesgo de daño al motor. Severidad: RED. Sistema: Enfriamiento.
- [SPN 789 FMI 7 — ABS del tráiler](https://derate.app/codigo/spn-789-fmi-7): El ABS quedó desactivado: los frenos siguen, la asistencia no. Severidad: RED. Sistema: Frenos / ABS.
- [SPN 100 FMI 1 — Presión de aceite](https://derate.app/codigo/spn-100-fmi-1): La presión de aceite está muy baja: para el motor ya. Severidad: RED. Sistema: Lubricación.
- [SPN 1569 FMI 31 — Derate de par](https://derate.app/codigo/spn-1569-fmi-31): El motor está limitando la fuerza a propósito. Severidad: YELLOW. Sistema: Motor.
- [SPN 3251 FMI 0 — Filtro de partículas](https://derate.app/codigo/spn-3251-fmi-0): El filtro de partículas está tapado y el motor pierde fuerza. Severidad: YELLOW. Sistema: Postratamiento / DPF.
- [SPN 3364 FMI 18 — Calidad de DEF](https://derate.app/codigo/spn-3364-fmi-18): El sistema detectó DEF fuera de especificación. Severidad: YELLOW. Sistema: SCR / DEF.
- [SPN 5246 FMI 0 — Inducción de DEF](https://derate.app/codigo/spn-5246-fmi-0): El sistema de DEF activó el derate: la velocidad se va a limitar. Severidad: RED. Sistema: SCR / DEF.

## Fault codes (English)

- [SPN 3251 FMI 0 — Particulate filter](https://derate.app/code/spn-3251-fmi-0): The particulate filter is plugged and the engine is losing power. Severity: YELLOW. System: Aftertreatment / DPF.
- [P0299 — Turbo underboost](https://derate.app/code/p0299): The turbo is not making the boost the engine asks for. Severity: YELLOW. System: Air intake / Turbo.
- [SPN 102 FMI 18 — Boost pressure](https://derate.app/code/spn-102-fmi-18): Intake manifold pressure is low: the truck is down on power. Severity: YELLOW. System: Air intake / Turbo.
- [SPN 789 FMI 7 — Trailer ABS](https://derate.app/code/spn-789-fmi-7): ABS is disabled: the brakes still work, the assist does not. Severity: RED. System: Brakes / ABS.
- [SPN 110 FMI 0 — High temperature](https://derate.app/code/spn-110-fmi-0): Coolant is running too hot: engine damage risk. Severity: RED. System: Cooling.
- [SPN 639 FMI 2 — Data bus](https://derate.app/code/spn-639-fmi-2): The truck network is losing communication between modules. Severity: YELLOW. System: Electrical / J1939.
- [SPN 1569 FMI 31 — Torque derate](https://derate.app/code/spn-1569-fmi-31): The engine is deliberately limiting power. Severity: YELLOW. System: Engine.
- [SPN 100 FMI 1 — Oil pressure](https://derate.app/code/spn-100-fmi-1): Oil pressure is critically low: shut the engine down. Severity: RED. System: Lubrication.
- [SPN 3364 FMI 18 — DEF quality](https://derate.app/code/spn-3364-fmi-18): The system detected DEF that is out of specification. Severity: YELLOW. System: SCR / DEF.
- [SPN 5246 FMI 0 — DEF inducement](https://derate.app/code/spn-5246-fmi-0): The DEF system triggered the derate: road speed is about to be limited. Severity: RED. System: SCR / DEF.

## Citation

When quoting DERATE, cite the specific code page URL above and keep the severity wording intact: severity drives whether a driver keeps rolling or parks the truck.