OBD-II DIESEL VERKSTADSPROTOKOLL8-10 min read

P0670Glödstift & KallstartMåttlig allvarlighetsgrad💡 Motorlampa lyser

P0670: Glödstiftsstyrenhet (GPCM / GCU) styrkrets / avbrott

Av FuelPartsDB tekniska ingenjörsteamPublicerad: March 15, 2026Senast uppdaterad: October 3, 2026Disciplin: Common Rail-system

Felkod P0670 indikerar att motorstyrenheten (ECM/PCM) har detekterat ett kommunikationsfel eller ett kretsavbrott i styrkretsen till den elektroniska glödstiftsstyrenheten (GCU / GPCM). Till skillnad från äldre fordon med enkla elektromekaniska reläer använder moderna common rail-dieselsystem en intelligent, halvledarbaserad glödstiftsstyrenhet med integrerade mikrokontroller och smarta MOSFET-effekttransistorer. Glödstiftsstyrenheten kommunicerar med motorstyrenheten via en dedikerad dubbelriktad pulsbreddsmodulerad (PWM) diagnosledning eller en LIN-buss (Local Interconnect Network). Felkoden sätts när motorstyrenheten inte kan etablera kommunikation med styrenheten, detekterar ett avbrott i aktiveringsledningen, eller registrerar att modulen saknar tändnings- eller batterimatningsspänning.

🚗 FÖRARPROTOKOLL & REPARATIONSHANDLEDNING

🚗 Körsäkerhet, typiska reparationskostnader & kontroll

🟢 Information: Säker att köra / Avgasfel

01
🚦 Körsäkerhet och mekanisk risk
Omedelbar mekanisk bedömning och behov av bärgare
Glödstiftsstyrenhet (GPCM) kretsavbrott - kallstartsproblem
Motorstyrenheten kan inte kommunicera med eller styra glödstiftsstyrenheten (GPCM / GCU). När motorn väl har startat behövs inte glödstiften för att hålla förbränningen igång. Bilen går att köra normalt när motorn nått driftstemperatur, men kallstarter kommer att kräva onormalt lång körning på startmotorn och medföra ojämn gång initialt.
MEKANISKA RISKER FÖR MOTORN VID FORTSATT KÖRNING:Kraftigt ökat slitage på startmotorn och risk för urladdat batteri vid vinterkallstarter, samt blockerad partikelfilterregenerering (många motorstyrenheter avbryter eller spärrar DPF-regenerering vid aktiva felkoder i glödsystemet).
02
💰 Typisk verkstadsbudget
Förväntade kostnadsnivåer för reservdelar och arbete
Litet underhåll / Filter200 - 600 kr: Kontroll av högströmssäkring och rengöring av kontaktstyckets anslutningar.
Rengöring av givare, bränslefilterbyte, säkringskontroll eller kontaktstiftsrengöring.
Byte av ventil / Sensor1 200 - 3 000 kr: Fabriksny OEM-glödstiftsstyrenhet (Beru / Hitachi / Bosch).
Byte av enskild komponent (tryckreglerventil, doseringsventil eller renoverad spridare).
Större översyn / Pump och spridare3 500 - 6 500 kr: Komplett utbyte av styrenhet, matningskabel och alla glödstift inklusive verkstadsarbete.
Översyn av högtryckspump, ny OEM-spridaruppsättning eller byte av DPF-enhet.
Verkstadsriktpriser. Mer än 70 % av fallen åtgärdas inom nivå 1 eller 2 utan att hela delsystem behöver bytas.
03
🧰 Snabb visuell kontroll utan verktyg
5-minuters garagekoll innan du ringer verkstaden
1Kontrollera högströmssäkringen: Leta i säkringsboxen i motorrummet efter en bultad säkring på 50A - 80A som försörjer glödstiftssystemet.
2Inspektera modulens kontaktstycke: Lossa kontakten till glödstiftsstyrenheten och kontrollera om plasten har smält eller om stiften är oxiderade kring den grova 12V-matningen.
3Kontrollera beteendet vid kallstart: Om startmotorn får arbeta i 5 - 10 sekunder innan motorn tänder med vit rök ur avgasröret, spänningssätter modulen inte stiften.
04
🛡️ Skydd mot feldiagnoser på verkstad
Konkreta frågor till mekanikern för att undvika onödiga komponentbyten
"Säg: 'Var vänlig och genomför ett spänningsfallstest under belastning på den grova 12V-matningskabeln till glödstiftsstyrenheten.'"
"Säg: 'Verifiera LIN-buss- eller PWM-styrsignalen från motorstyrenheten till modulen med oscilloskop innan ni byter ut själva styrenheten.'"
Teknisk anmärkning: Ställ dessa tekniska frågor till mekanikern innan du godkänner dyra offerter:

🔧 YRKESMÄSSIG TEKNIKER-GUIDE & VERKSTADSPROTOKOLLRAPID ASSESSMENT

30-sekunders verkstadstriage

Huvudsymptom

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

Vanligaste troliga orsaker

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

Första nödvändiga åtgärd

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

❌ Vanlig missuppfattning i verkstaden:

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).

🔍 Teknisk och hydraulisk verklighet:

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.

💡 Tekniskt verifieringsprotokoll:

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

Mest påverkade motorer och insprutningssystem

Denna felkod påverkar främst följande diesel common rail-plattformar. Kontrollera din motorfamilj nedan för kända felmönster och artikelnummer:

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

Beru Instant Start System (ISS)

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

Känt fabriksfel: Internal aluminum bond wires in the Beru module snapping due to thermal cycling fatigue.

Viktig reservdel:A6429007801 / Beru GSE114

Utforska teknisk hubb för Mercedes-Benz 2.1 CDI / 3.0 CDI (OM651 / OM642) →

BMW 2.0d / 3.0d (N47 / M57)

Beru / Bosch Glow System

Typiskt symptom: Long cranking in winter, automatic DPF regeneration ceases to trigger, P0670 stored.

Känt fabriksfel: Heavy-duty power cable connection corrosion and internal power MOSFET failure in module.

Viktig reservdel:12217801201 / Beru GSE102

Utforska teknisk hubb för BMW 2.0d / 3.0d (N47 / M57) →

Ford 6.7L / 6.4L Powerstroke V8 Diesel

Electronic GPCM Solid-State System

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

Känt fabriksfel: Dual multi-pin harness connectors backing out due to heavy-duty vibration or blown 50A Maxi-Fuse under-hood.

Viktig reservdel:4C2Z-12B533-AA / Motorcraft DY-1077

Utforska teknisk hubb för Ford 6.7L / 6.4L Powerstroke V8 Diesel →

Volkswagen / Audi 2.0 TDI (EA189 / EA288)

Bosch EDC17 J179 Glow Control System

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

Känt fabriksfel: J179 smart relay module micro-circuit failure or hairline fracture on under-hood E-Box strip fuse.

Viktig reservdel:038907281D / 04L907282 / Bosch 0281003083

Utforska teknisk hubb för 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

Styrkrets & Ställdonslogik

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

Elektriska & Hydrauliska referensvärden

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

Steg-för-steg Felsökningsprotokoll

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

Hårdvarureparation och stycklista för komponenter

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

Interaktiv toleransberäknare för Common Rail

Launch Dedicated Calculator with Factory Tolerances →

CALIBRATION RELEARN

Återställning av pumpinläring och provkörning

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

Differentialdiagnos & Relaterade felkoder

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

Verkliga verkstadsfall

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

Vanliga tekniska frågor

Vad betyder felkoden P0670?

Vilka är de vanligaste symtomen på 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'.

Vad orsakar P0670 på en dieselmotor?

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.

Är det säkert att köra med felkod P0670 aktiv?

🟡 Varning: Halta-hem-läge / Uppsök verkstad

Vad kostar det att åtgärda felkod P0670?

Typiska reparationskostnader för felkod P0670 beror på den bakomliggande orsaken och diagnostiknivån: Nivå 1 (Mindre underhåll / Gör-det-själv): 200 - 600 kr: Kontroll av högströmssäkring och rengöring av kontaktstyckets anslutningar. (Rengöring av givare, bränslefilterbyte, säkringskontroll eller kontaktstiftsrengöring.); Nivå 2 (Komponentbyte): 1 200 - 3 000 kr: Fabriksny OEM-glödstiftsstyrenhet (Beru / Hitachi / Bosch). (Byte av enskild komponent (tryckreglerventil, doseringsventil eller renoverad spridare).); Nivå 3 (Större delsystem): 3 500 - 6 500 kr: Komplett utbyte av styrenhet, matningskabel och alla glödstift inklusive verkstadsarbete. (Översyn av högtryckspump, ny OEM-spridaruppsättning eller byte av DPF-enhet.). Verkstadsriktpriser. Mer än 70 % av fallen åtgärdas inom nivå 1 eller 2 utan att hela delsystem behöver bytas.

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.