PROTOCOLLO D'OFFICINA DIESEL OBD-II8-10 min read

P0670Candelette e AvviamentoGravità Moderata💡 Spia motore accesa

P0670: Circuito di comando centralina candelette di preriscaldo (GPCM / GCU) / Aperto

Dal team di ingegneria tecnica FuelPartsDBPubblicato: March 15, 2026Ultimo aggiornamento: October 3, 2026Disciplina: Sistemi Common Rail

Il codice di guasto diagnostico (DTC) P0670 indica che la centralina gestione motore (ECM/PCM) ha rilevato un'anomalia di comunicazione elettrica o un'interruzione di continuità nel circuito di comando verso la centralina candelette (GCU / GPCM). A differenza dei sistemi meno recenti basati su relè elettromeccanici tradizionali, i moderni motori diesel common rail impiegano una centralina a stato solido integrata con microcontrollori dedicati e MOSFET di potenza intelligenti. La GCU dialoga costantemente con la centralina motore tramite una linea diagnostica bidirezionale a modulazione di larghezza di impulso (PWM) o un bus seriale monofilo LIN (Local Interconnect Network). Il DTC P0670 viene impostato quando l'ECM non riceve risposta dalla GCU, rileva un circuito aperto sulla linea di consenso (enable) oppure riscontra l'assenza della tensione di alimentazione principale sotto chiave o da batteria sul modulo.

🚗 PROTOCOLLO GUIDATORE & RIPARAZIONE

🚗 Sicurezza operativa, costi tipici e verifica diagnostica

🟢 Avviso: Marcia sicura / Controllo emissioni

01
🚦 Sicurezza di guida e rischi meccanici
Valutazione immediata e necessità di carro attrezzi
Circuito centralina candelette (GPCM) aperto - Anomalia avviamento a freddo
La centralina motore non riesce a pilotare né a interrogare il modulo di comando candelette (GPCM / GCU). Nei motori ad accensione per compressione a regime termico, l'apporto delle candelette non è necessario per il funzionamento del motore, rendendo possibile la marcia regolare a caldo. Tuttavia, gli avviamenti a motore freddo comporteranno trascinamenti prolungati del motorino di avviamento e funzionamento ruvido nei primi minuti.
PERICOLI MECCANICI IN CASO DI GUIDA CONTINUA:Forte usura del motorino di avviamento e scarica rapida della batteria a causa dei prolungati cicli di avviamento invernale; blocco della rigenerazione del filtro antiparticolato DPF/FAP (molte strategie software ECU inibiscono la rigenerazione in presenza di guasti attivi sul preriscaldo/post-riscaldo).
02
💰 Budget tipico di riparazione in officina
Scaglioni di costo per ricambi e manodopera
Manutenzione leggera / Filtro20€ - 60€: Verifica del maxifusibile di potenza, ripristino masse e pulizia contatti del connettore elettrico.
Pulizia sensore, sostituzione filtro carburante, controllo fusibili o contatti cablaggio.
Sostituzione valvola / Sensore120€ - 280€: Sostituzione della centralina candelette con ricambio originale o equivalente di primo impianto (Beru / Hitachi / Bosch).
Sostituzione singolo componente (valvola regolatrice, unità dosatrice o iniettore revisionato).
Revisione complessa / Pompa e iniettori350€ - 600€: Sostituzione completa di centralina preriscaldo, cablaggio di alimentazione ad alto amperaggio e kit candelette motore.
Revisione pompa alta pressione, set iniettori nuovi o sostituzione gruppo DPF.
Tariffe indicative di officina. Oltre il 70% dei casi si risolve al Livello 1 o 2 senza sostituire interi sottogruppi.
03
🧰 Verifiche visive rapide fai-da-te
Controllo rapido in 5 minuti senza attrezzi prima di chiamare l'officina
1Verifica del maxifusibile ad alto amperaggio: individuare nella scatola fusibili vano motore il fusibile a vite (bolt-down) da 50A - 80A che alimenta lo stadio di potenza delle candelette.
2Controllo del connettore di alimentazione: scollegare il connettore multipolare dalla centralina candelette e verificare l'assenza di sfiammature, ossido o plastica fusa sul pin di potenza a 12V.
3Osservazione dell'avviamento a freddo: verificare se a temperature rigide il motore richiede 5-10 secondi di trascinamento seguiti da zoppicamento iniziale e fumo bianco/grigio di gasolio incombusto allo scarico.
04
🛡️ Protezione contro diagnosi errate in officina
Domande mirate per evitare la sostituzione inutile di componenti
"Dite: 'Verificate la presenza di cadute di tensione sotto carico sul cavo principale di alimentazione a 12V proveniente dalla batteria prima di sostituire la centralina.'"
"Dite: 'Prima di dichiarare guasto il modulo, controllate con oscilloscopio l'integrità del segnale di comando PWM o del bus di comunicazione LIN proveniente dalla ECU motore.'"
Nota tecnica: Poni queste domande al meccanico prima di autorizzare costose sostituzioni:

🔧 PROTOCOLLO TECNICO PROFESSIONALE & OFFICINARAPID ASSESSMENT

Triage d'officina in 30 secondi

Sintomi principali

Check Engine Light (MIL) and flashing glow plug spiral indicator illuminated on the dashboard
Prolonged engine cranking and hard starting when ambient temperature drops below 10°C (50°F)
Rough, irregular idle with severe engine vibration during the first minute after cold start

Cause più probabili

Internal electronic component failure, blown MOSFET driver, or solder joint fatigue inside the Glow Control Unit (GCU)
Blown high-current 60A-80A maxi-fuse supplying main battery power to the Glow Control Unit
Blown low-current ignition fuse (typically 5A-10A) supplying wake-up power to GCU Terminal 15

Prima azione richiesta

Connect scan tool live telemetry: compare Target Fuel Rail Pressure vs Actual Rail Pressure and log metering valve command PWM duty cycle during idle and road load.

🛠️ Common Rail Pressure & Flow Converter

Expensive Diagnostic Pitfall & Technical Reality

❌ Errore comune in officina:

P0670 requires replacing all 4/6 glow plugs at high cost, and if plugs are stuck in the cylinder head, head removal is required ($1,500 - $2,500).

🔍 Realtà tecnica e idraulica:

P0670 is NOT an individual glow plug fault (which are P0671 - P0678). P0670 means the ECM cannot communicate with the Glow Plug Control Module (GPCM) over the dedicated bidirectional LIN-Bus or PWM control wire. The glow plugs themselves are almost never damaged by this code. In over 85% of cases, the fault is caused by an unseated/corroded multi-pin GPCM connector, a blown small 10A ignition fuse that powers the module's micro-controller logic, or water ingress corroding the module pins under the battery tray.

💡 Protocollo di verifica tecnica:

Spending $1,200+ attempting to pull delicate glow plugs (risking sheared threads in head) vs replacing a $15 control fuse or an $85 plug-and-play Beru/Hitachi module located safely on the firewall, saving over $1,100.

Low-Voltage Ceramic Plug Burnout & Tip Fracture Alert

CRITICAL WORKSHOP WARNING: Never apply direct 12V battery power to test glow plugs on vehicles equipped with electronic GCUs!

MANDATORY PROTOCOL: Modern common rail diesel engines (e.g. BMW, Mercedes, VW, Ford) employ low-voltage ceramic or rapid-heating metallic glow plugs rated for only 4.4V, 5.0V, or 7.0V DC. If a technician attempts a bench test by connecting a 12V battery directly across the plug, the extreme over-voltage causes the ceramic heating tip to shatter or vaporize in less than 2 seconds! If this is done with the plug inside the engine, ceramic shards drop into the cylinder, destroying the piston crown and turbocharger turbine wheel.

PLATFORM ARCHITECTURE

Motori e piattaforme di iniezione più colpiti

Questo codice di guasto interessa principalmente le seguenti piattaforme diesel common rail. Verificate di seguito la famiglia di motori per le anomalie tipiche e i codici ricambio:

Mercedes-Benz 2.1 CDI / 3.0 CDI (OM651 / OM642)

Beru Instant Start System (ISS)

Sintomo tipico: Glow plug coil light stays illuminated for 60 seconds AFTER start-up, P0670 stored.

Anomalia tipica di fabbrica: Internal aluminum bond wires in the Beru module snapping due to thermal cycling fatigue.

Componente chiave:A6429007801 / Beru GSE114

Esplora l'hub tecnico per Mercedes-Benz 2.1 CDI / 3.0 CDI (OM651 / OM642) →

BMW 2.0d / 3.0d (N47 / M57)

Beru / Bosch Glow System

Sintomo tipico: Long cranking in winter, automatic DPF regeneration ceases to trigger, P0670 stored.

Anomalia tipica di fabbrica: Heavy-duty power cable connection corrosion and internal power MOSFET failure in module.

Componente chiave:12217801201 / Beru GSE102

Esplora l'hub tecnico per BMW 2.0d / 3.0d (N47 / M57) →

Ford 6.7L / 6.4L Powerstroke V8 Diesel

Electronic GPCM Solid-State System

Sintomo tipico: Extended cold cranking accompanied by white smoke clouds, Wrench Light active with P0670.

Anomalia tipica di fabbrica: Dual multi-pin harness connectors backing out due to heavy-duty vibration or blown 50A Maxi-Fuse under-hood.

Componente chiave:4C2Z-12B533-AA / Motorcraft DY-1077

Esplora l'hub tecnico per Ford 6.7L / 6.4L Powerstroke V8 Diesel →

Volkswagen / Audi 2.0 TDI (EA189 / EA288)

Bosch EDC17 J179 Glow Control System

Sintomo tipico: Flashing glow plug spiral indicator on cluster, delayed winter starting, P0670 stored in ECU.

Anomalia tipica di fabbrica: J179 smart relay module micro-circuit failure or hairline fracture on under-hood E-Box strip fuse.

Componente chiave:038907281D / 04L907282 / Bosch 0281003083

Esplora l'hub tecnico per Volkswagen / Audi 2.0 TDI (EA189 / EA288) →

WORKSHOP MASTER TEARDOWN GUIDE

Diesel Glow Plug Diagnostics & Circuit Troubleshooting Guide

Workshop troubleshooting guide for diesel glow plug fault codes P0380, P0670, and P0671 to P0674. Resistance specs, GPCM relay testing, and removal torque.

Read Full Master Guide →

THEORY OF OPERATION

Circuito di controllo e logica attuatore

1. Dynamic In-Demand Fuel Metering

The electronic Glow Control Unit (GCU) operates as a slave node on the vehicle's electronic architecture. It connects via two primary harnesses: a high-current connector (receiving unswitched battery positive through a 60A-80A maxi-fuse and outputting individual current lines to each cylinder's glow plug) and a low-current control connector (incorporating 12V ignition wake-up, logic ground, and the LIN-bus / PWM communication line to the ECM). The GCU modulates individual glow plug voltages (varying from 4.4V to 11V DC depending on plug type) to achieve fast heating in under 2 seconds while preventing element burnout.

2. Closed-Loop PID Deviation Monitoring

During every ignition cycle, the ECM transmits initialization commands over the LIN-bus / PWM interface to verify GCU internal self-test status. The GCU responds with module identification, operating status, and individual cylinder current feedback. If the ECM receives no response within 500 to 1,000 milliseconds, or if the control wire voltage is pulled continuously to ground or floats open at 12V, the ECM records DTC P0670. The ECM disables all pre-heating, post-heating, and DPF regeneration intermediate heating routines.

3. Diagnostic Trap: Normally Open (NO) vs Normally Closed (NC) Valves

Electronic GCU Failsafe Shutdown: When a communication loss or control circuit fault occurs (P0670), the GCU internal micro-controller immediately de-energizes all internal MOSFET output stages to prevent uncontrolled continuous heating that would melt the glow plugs. Consequently, the glow plugs remain completely inoperative until communication and power are restored.

ENGINEERING SPECIFICATIONS

Parametri fisici elettrici ed idraulici

Solenoid Coil DC ResistanceCeramic Glow Plug Cold Resistance: 0.3 - 0.5 Ω @ 20°C; Metallic Low-Voltage Plug: 0.5 - 0.9 ΩMeasured @ 20°C across terminals 1 & 2

Insulation Resistance> 10 MΩ measured between any GCU terminal pin and module metal heatsink (tested @ 250V/500V DC)Between terminals and pump body (ground)

Operating Supply VoltageGCU Main Battery Supply (Terminal 30): 12.0 V - 14.5 V DC; Switched Ignition Supply (Terminal 15): > 11.8 VHigh-side feed from ECM / main relay

PWM Frequency StandardLIN-bus serial communication (19.2 kbaud) or bidirectional PWM square wave (10 Hz - 100 Hz)Square-wave PWM modulation

Idle Duty Cycle (Warm Engine)LIN-bus Signal Voltage Levels: Dominant Low: < 1.5 V DC; Recessive High: > 10.5 V DC (Battery level)Nominal baseline at 250–350 bar

Full-Load Duty Cycle (WOT)GCU Maximum Operating Capacity: Up to 35 A per channel peak inrush; 12 A continuous holding currentMaximum high-speed fuel delivery demand

Low-Pressure Feed SupplyMaximum Permissible Control Wire Resistance: < 0.4 Ω end-to-end between ECM pin and GCU connectorMeasured at pump fuel inlet

Internal Cascade BackpressureModule Ground Circuit Resistance: < 0.3 Ω measured between GCU chassis ground pin and battery negativeControlled by overflow cascade valve

PROCEDURAL PROTOCOL

Protocollo di Diagnosi d'Officina Passo Passo

STEP 1

Verify Main Battery Power & Ignition Wake-Up Feeds at GCU

Locate the Glow Control Unit (typically mounted on the engine block, wheel arch, or near the battery). Disconnect the module connectors. Using a digital multimeter referenced to battery negative, test the large red battery positive wire (Terminal 30); it must read constant battery voltage (> 12.2V). Turn ignition ON and test the switched ignition wire (Terminal 15); it must read > 11.8V. If 0V, inspect fuses.

STEP 2

Test GCU Chassis Ground Circuit Integrity

With the connector unplugged and ignition OFF, measure resistance between the module ground terminal and the battery negative terminal using the multimeter 200 Ω scale. Resistance must be < 0.3 Ω. Perform a voltage drop test under load to verify that high-current return is clean and uncorroded.

STEP 3

Oscilloscope LIN-Bus / PWM Communication Signal Verification

Reconnect the GCU. Back-probe the communication line connecting the ECM to the GCU with an oscilloscope. Switch ignition ON. For LIN-bus architectures: you must observe a crisp digital square wave pulsing between dominant low (< 1.5V) and recessive high (battery voltage ~12V) at 19.2 kbaud. A flat line at 0V indicates a short to ground; a flat line at 12V indicates an open circuit or inactive ECM.

STEP 4

Harness Continuity & Short-to-Ground Test

Disconnect the main harness connector from the ECM and the small control connector from the GCU. Measure continuity on the communication wire between ECM and GCU pins (< 0.4 Ω). Check resistance to chassis ground (must read infinite / OL). Check for short to 12V.

STEP 5

Scan Tool Bi-Directional GCU Activation Test

Using an OEM diagnostic scan tool, navigate to Special Functions -> 'Glow Control Module Actuation Test'. Command the module ON while measuring voltage at the glow plug harness caps. The module should output pulsed voltage to all channels. If power and communication are good but no voltage is output, the GCU has suffered internal MOSFET failure.

STEP 6

Inspect Connector Pins for Water Intrusion & Corrosion

Inspect the multi-pin connector on the GCU for green copper corrosion or backed-out pins. Because the GCU is often mounted low on the engine or near splash shields, water intrusion through degraded silicone seals is a very common root cause of P0670.

COMPONENT-LEVEL REPAIR

Riparazione hardware e distinta base componenti

Preheating Electronic Control & LIN-Bus Communication Architecture

Hitachi / Beru Smart Glow Plug Control Module (GPCM)

GSE102 / 0 522 120 702 / A6429005801

Solid-state electronic power stage with onboard microprocessor communicating with ECM over LIN

OEM: Protocol: Replace if internal power MOSFETs short out or LIN communication fails with verified 12V/Ground

GPCM Logic Stage 10A Blade Fuse (Mini / Low-Profile)

Littelfuse Mini 10A Red / Underhood Fuse Box

Supplies switched +12V battery power to the module's internal logic microprocessor

OEM: Protocol: Inspect visually with test light; replace if filament is blown

Multi-Pin Sealed GPCM Harness Loom Connector Plug

Tyco / AMP 12-Pin Heavy-Duty Timer Connector

Carries high-current glow feeds and low-voltage LIN-Bus communication lines

OEM: Protocol: Clean or replace if terminals show green copper oxidation or moisture water entry

Workshop Technical & Economic Benchmark: GPCM mounting bolts M6: 8 - 9 Nm; Multimeter with Hz/Duty-cycle function (measure LIN-bus: should toggle between 9V - 11V at key on).

LIVE WORKSHOP TOOL

Calcolatore interattivo tolleranze Common Rail

Launch Dedicated Calculator with Factory Tolerances →

CALIBRATION RELEARN

Reset adattamento pompa AP & Ciclo di apprendimento

Following the replacement of the Glow Control Unit (GCU) or repair of its communication wiring for DTC P0670:

1. Clear all trouble codes from the Engine Control Module memory using an OBD-II diagnostic tool.

2. Access ECM Special Functions -> 'Glow Control Unit Identification / Adaptation'. Confirm that the ECM successfully queries and reads the hardware and software part numbers of the new GCU over the LIN-bus.

3. Switch ignition OFF for 60 seconds to allow the ECM main relay to power down and register the new module.

4. Switch ignition ON with a cold engine and verify that the spiral glow indicator illuminates and extinguishes in accordance with ambient temperature.

5. Start the engine and verify smooth, immediate idle without misfires, followed by clearing of all emissions readiness monitors.

DIFFERENTIAL DIAGNOSIS

Diagnosi differenziale e codici correlati

P0380

Glow Plug/Heater Circuit 'A' Malfunction

P0671

Cylinder 1 Glow Plug Circuit / Open

U0106

Lost Communication with Glow Plug Control Module

P2458

Diesel Particulate Filter Regeneration Duration

FIELD REPAIR REPORTS

Casi pratici d'officina

CASE #1

2013 Mercedes-Benz ML350 BlueTEC (W166 OM642 3.0 V6)(192,000 km)

Reported Complaint:Prolonged cold start cranking in winter; glow plug spiral icon relights for 60 seconds after engine starts; DTC P0670 logged.

Teardown Root Cause:Tested Beru preheating module main battery post: 12.4V present. Disconnected 12-pin control harness and found Pin 4 (switched ignition Terminal 15 feed) had 0V. Traced wiring diagram to engine bay fuse box: the 10A module logic fuse had blown due to moisture oxidation in the fuse holder.

Repair Solution:Cleaned fuse terminal socket and installed new 10A fuse. Terminal 15 voltage restored to 12.4V and LIN-Bus communication signal verified at 10.5V. Engine cold start was instantaneous with zero fault codes.

DIAGNOSTIC FAQ

Domande tecniche frequenti

Cosa significa il codice guasto motore P0670?

Quali sono i sintomi più frequenti di P0670?

Check Engine Light (MIL) and flashing glow plug spiral indicator illuminated on the dashboard, Prolonged engine cranking and hard starting when ambient temperature drops below 10°C (50°F), Rough, irregular idle with severe engine vibration during the first minute after cold start, Clouds of acrid white or grey exhaust smoke emitted during cold start cranking, Automatic DPF soot regeneration completely disabled, leading to progressive particulate filter restriction, Diagnostic scan tool reports 'No Communication with Glow Plug Control Module' or 'GPCM Circuit Open'.

Cosa causa P0670 in un motore diesel?

Internal electronic component failure, blown MOSFET driver, or solder joint fatigue inside the Glow Control Unit (GCU); Blown high-current 60A-80A maxi-fuse supplying main battery power to the Glow Control Unit; Blown low-current ignition fuse (typically 5A-10A) supplying wake-up power to GCU Terminal 15; Severed, broken, or chafed LIN-bus / PWM communication wire between the ECM and the GCU; Corroded, oxidized, or water-damaged terminal pins inside the GCU electrical harness connectors; Corroded or loose module chassis ground cable preventing the GCU internal logic from powering up.

È sicuro guidare con il codice P0670 attivo?

🟡 Attenzione: Modalità emergenza / Rivolgersi a officina

Quanto costa riparare il codice di guasto P0670?

I costi tipici di riparazione per il codice P0670 dipendono dalla causa principale e dal livello di diagnosi: Livello 1 (Manutenzione minore / Fai da te): 20€ - 60€: Verifica del maxifusibile di potenza, ripristino masse e pulizia contatti del connettore elettrico. (Pulizia sensore, sostituzione filtro carburante, controllo fusibili o contatti cablaggio.); Livello 2 (Sostituzione componente): 120€ - 280€: Sostituzione della centralina candelette con ricambio originale o equivalente di primo impianto (Beru / Hitachi / Bosch). (Sostituzione singolo componente (valvola regolatrice, unità dosatrice o iniettore revisionato).); Livello 3 (Gruppo principale): 350€ - 600€: Sostituzione completa di centralina preriscaldo, cablaggio di alimentazione ad alto amperaggio e kit candelette motore. (Revisione pompa alta pressione, set iniettori nuovi o sostituzione gruppo DPF.). Tariffe indicative di officina. Oltre il 70% dei casi si risolve al Livello 1 o 2 senza sostituire interi sottogruppi.

Can I replace an electronic GCU with a standard 4-pin relay?

Absolutely not. Modern common rail diesel ECMs communicate with the GCU via microsecond LIN-bus data telegrams and require closed-loop current feedback for each individual cylinder. Installing an analog relay will destroy communication, keep P0670 permanently active, and burn out low-voltage glow plugs.

Why does a faulty GCU prevent DPF regeneration?

Modern common rail engines activate the glow plugs during DPF active regeneration to stabilize in-cylinder post-injection combustion and add heavy electrical load onto the alternator to elevate exhaust temperatures. If the ECM cannot control the GCU, it aborts all DPF regenerations as a safety precaution.

Where is the Glow Control Module usually located?

Depending on vehicle make, the GCU is typically bolted to the engine block underneath the intake manifold (e.g. BMW M47/M57/N47/N57), mounted on the engine bay bulkhead near the brake booster (e.g. Mercedes CDI, VAG TDI), or located inside the under-hood battery fuse distribution box.