Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / B2406 — STL.unit comm.(PTC operate)

B2406 — STL.unit comm.(PTC operate)

Detailed page for trouble code B2406.

32,983codes
59brands
10,522generic
22,461specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
Reset
Code

B2406

MITSUBISHI B — Body

STL.unit comm.(PTC operate)

Brand: MITSUBISHI
Type: B — Body
Views: UK: 8 EN: 11 RU: 13
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open, short or intermittent wiring between modules (power, ground or communication lines)
  • Faulty connector (corrosion, bent pins, poor contact)
  • Failed STL/PTC control unit or related HVAC/BCM module
  • Blown fuse or faulty relay supplying PTC/STL unit
  • CAN/LIN bus wiring fault or missing termination
  • Battery voltage too low during attempt to operate PTC

Symptoms

  • PTC (auxiliary) heater does not activate when commanded
  • HVAC takes longer to produce heat or reduced cabin heating
  • Related warning lamp or message on dash (HVAC/aux heater)
  • Stored B2406 code and possibly other communication DTCs
  • Erratic operation of HVAC or automatic climate control functions

What to check

  • Read freeze frame and full DTC list with a capable scan tool; note any other communication codes
  • Verify battery voltage is within normal range (engine off and cranking conditions)
  • Inspect fuses and relays for PTC/STL and HVAC/BCM circuits
  • Visually inspect connectors and harnesses at the STL/PTC unit and associated modules for corrosion, damage or loose pins
  • Check for activity on the vehicle communication bus (CAN/LIN) with a scan tool or oscilloscope
  • Measure supply voltage and ground continuity at the STL/PTC unit connector

Signal parameters

  • Supply voltage to STL/PTC unit: nominal battery voltage ~11–14.5 V when engine running
  • Ground: continuity to chassis ground, resistance should be very low (
  • CAN bus idle differential: both lines ~2.5 V nominal with expected differential behavior during communication (use scope/scan tool)
  • LIN bus idle: typically near battery voltage with pull-down signaling (verify with vehicle-specific reference)
  • PTC heater current draw: can be high when active (tens of amps depending on heater design) — verify using appropriate in-line current measurement
  • PTC element resistance: low ohms (measure against manufacturer spec in service literature)

Diagnostic algorithm

  1. Connect a diagnostic scan tool, read and record all related DTCs and freeze frame data. Clear codes and attempt to reproduce.
  2. Verify battery condition and voltage. Recharge or replace if low and repeat test.
  3. Check fuses/relays for PTC/STL and HVAC circuits; replace if faulty.
  4. Inspect and secure connectors at the STL/PTC unit, HVAC control module and BCM. Repair corrosion or damaged pins.
  5. With the scan tool, attempt to command the PTC on/off while monitoring module responses and communication bus traffic.
  6. Check power and ground at the STL/PTC unit connector with meter; repair any open circuits.
  7. Probe CAN/LIN lines with a scope or breakout box: confirm idle voltages, data frames and proper termination (approx. 60 Ω across CANH/CANL for CAN bus).
  8. Measure PTC heater resistance and, if safe and specified, measure current draw during operation. Compare to service specifications.
  9. Perform continuity and short checks on the wiring harness between relevant modules. Repair any damaged wiring.
  10. If wiring and power/ground are good but communication is absent or corrupted, consider replacing the STL/PTC control unit or the communicating module per service manual. Reprogram/relearn as required.
  11. After repairs, clear codes and verify normal operation through several test cycles; monitor for reappearance of B2406 or related codes.

Likely causes

  • Loose or corroded connector at the STL/PTC unit
  • Open or short on CAN or LIN communication line to the STL unit
  • Failed STL/PTC control unit
  • Missing 12 V supply or ground to the STL/PTC unit (faulty fuse/relay)
  • Intermittent wiring harness damage (chafing, water intrusion)

Fault status

⚠️ Status
Communication error: STL unit did not respond or communication failed while PTC heater operation was requested. Check power, ground, connectors, wiring and network communications.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

B2400 B2401 B2402 B2403 B2405 B2407
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

B2406

Other B — Body

Audio Single-Disc CD Player Internal Fault

Brand: Other
Type: B — Body
Views: UK: 13 EN: 25 RU: 19
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open, short or intermittent wiring between modules (power, ground or communication lines)
  • Faulty connector (corrosion, bent pins, poor contact)
  • Failed STL/PTC control unit or related HVAC/BCM module
  • Blown fuse or faulty relay supplying PTC/STL unit
  • CAN/LIN bus wiring fault or missing termination
  • Battery voltage too low during attempt to operate PTC

Symptoms

  • PTC (auxiliary) heater does not activate when commanded
  • HVAC takes longer to produce heat or reduced cabin heating
  • Related warning lamp or message on dash (HVAC/aux heater)
  • Stored B2406 code and possibly other communication DTCs
  • Erratic operation of HVAC or automatic climate control functions

What to check

  • Read freeze frame and full DTC list with a capable scan tool; note any other communication codes
  • Verify battery voltage is within normal range (engine off and cranking conditions)
  • Inspect fuses and relays for PTC/STL and HVAC/BCM circuits
  • Visually inspect connectors and harnesses at the STL/PTC unit and associated modules for corrosion, damage or loose pins
  • Check for activity on the vehicle communication bus (CAN/LIN) with a scan tool or oscilloscope
  • Measure supply voltage and ground continuity at the STL/PTC unit connector

Signal parameters

  • Supply voltage to STL/PTC unit: nominal battery voltage ~11–14.5 V when engine running
  • Ground: continuity to chassis ground, resistance should be very low (
  • CAN bus idle differential: both lines ~2.5 V nominal with expected differential behavior during communication (use scope/scan tool)
  • LIN bus idle: typically near battery voltage with pull-down signaling (verify with vehicle-specific reference)
  • PTC heater current draw: can be high when active (tens of amps depending on heater design) — verify using appropriate in-line current measurement
  • PTC element resistance: low ohms (measure against manufacturer spec in service literature)

Diagnostic algorithm

  1. Connect a diagnostic scan tool, read and record all related DTCs and freeze frame data. Clear codes and attempt to reproduce.
  2. Verify battery condition and voltage. Recharge or replace if low and repeat test.
  3. Check fuses/relays for PTC/STL and HVAC circuits; replace if faulty.
  4. Inspect and secure connectors at the STL/PTC unit, HVAC control module and BCM. Repair corrosion or damaged pins.
  5. With the scan tool, attempt to command the PTC on/off while monitoring module responses and communication bus traffic.
  6. Check power and ground at the STL/PTC unit connector with meter; repair any open circuits.
  7. Probe CAN/LIN lines with a scope or breakout box: confirm idle voltages, data frames and proper termination (approx. 60 Ω across CANH/CANL for CAN bus).
  8. Measure PTC heater resistance and, if safe and specified, measure current draw during operation. Compare to service specifications.
  9. Perform continuity and short checks on the wiring harness between relevant modules. Repair any damaged wiring.
  10. If wiring and power/ground are good but communication is absent or corrupted, consider replacing the STL/PTC control unit or the communicating module per service manual. Reprogram/relearn as required.
  11. After repairs, clear codes and verify normal operation through several test cycles; monitor for reappearance of B2406 or related codes.

Likely causes

  • Loose or corroded connector at the STL/PTC unit
  • Open or short on CAN or LIN communication line to the STL unit
  • Failed STL/PTC control unit
  • Missing 12 V supply or ground to the STL/PTC unit (faulty fuse/relay)
  • Intermittent wiring harness damage (chafing, water intrusion)

Fault status

⚠️ Status
Communication error: STL unit did not respond or communication failed while PTC heater operation was requested. Check power, ground, connectors, wiring and network communications.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

B2400 B2401 B2402 B2403 B2405 B2407
Workshop Manuals

Available brands with manuals

2
AUDI 11

6-speed manual gearbox 0B1, front-wheel drive — Workshop Manual (Edition 05.2014)

Workshop Manual
Years: 2008 Manual in English Pages: 187 4.9 MB
Short description

Workshop manual for the 6‑speed manual gearbox 0B1 (front‑wheel drive). Includes identification, technical data, gearbox/selector removal & installation procedures, clutch hydraulics, adjustment instructions and front differential service. Applicable to Audi A4, Audi A5 (Coupé, Cabriolet, Sportback) and Audi Q5 as referenced in the manual. Edition: 05.2014.

199,00 UAH
Contents
Key sections:
  • 00 - Technical data
  • 1 Identification
  • 1.1 Gearbox identification
  • 2 Technical data
  • 2.1 Allocation of gearbox to engine
  • 2.1.1 Allocation - Audi A4 2008 ►
  • 2.1.2 Allocation - Audi A5 Coupé 2008 ►, Audi A5 Sportback 2010 ►
  • 2.1.3 Allocation - Audi A5 Cabriolet 2009 ►
  • 2.1.4 Allocation - Audi Q5 2008 ►
  • 2.2 Capacities
  • 3 Transmission layout
  • 3.1 Transmission layout - front‑wheel drive
Buy

Audi A3 (1997) – 1.6L 4-cylinder (2‑valve) Engine Mechanical Components Service Manual (AEH, AKL, APF) – Edition 07.2002

Workshop Manual
Years: 1997 Manual in English Pages: 283 4.3 MB
Short description

Service manual for Audi A3 (1997) 1.6L 4‑cylinder (2‑valve) engines (codes AEH, AKL, APF). Includes technical data, engine removal/installation, crankshaft group, cylinder head and valve gear, lubrication, cooling and exhaust system procedures. Edition 07.2002.

199,00 UAH
Contents
Key sections:
  • 00 - Technical data ............................................................1
  • 1 Technical data ............................................................1
  • 1.1 Technical data .......................................................1
  • 1.2 Engine number .......................................................1
  • 1.3 Engine data ........................................................1
  • 10 - Removing and installing engine ..........................................3
  • 1 Removing and installing engine .........................................3
  • 1.1 Removing and installing engine ....................................3
  • 1.2 Removing - vehicles with engine codes AEH, AKL .....................4
  • 1.3 Removing - vehicles with engine code APF ..........................18
  • 1.4 Detaching engine from gearbox ...................................35
  • 1.5 Attaching engine to repair stand ................................38
Buy

AUDI A3 (2004) Workshop Manual — 2.0L FSI Turbo (4‑cyl, 4‑valve) Engine, Mechanics — Edition 03.2017

Workshop Manual
Years: 2004 Manual in English Pages: 235 3.8 MB
Short description

Official workshop manual for the Audi A3 2.0L FSI turbo engine (mechanics). Includes step‑by‑step removal/install procedures, technical data, tightening torques and diagnostic/repair instructions. Intended for professional garages and experienced technicians.

199,00 UAH
Contents
Key sections:
  • 00 - Technical data
  • 1 Engine number
  • 2 Engine data (code letters AXX, BPY, BWA, BHZ, BZC, CDL — capacity, power, torque, bore/stroke, compression, ignition)
  • 3 Safety precautions
  • 3.1 Working on the fuel system
  • 3.2 Procedure before opening high-pressure section
  • 3.3 Working on the cooling system
  • 3.4 Using testers during road test
  • 3.5 Working on the exhaust system
  • 4 General repair instructions
  • 4.1 Cleanliness rules for fuel/injection/turbo
  • 4.2 Checking fuel system for leaks
Buy

Audi A3 2004 — Electrical System (Workshop Manual, Edition 02.2018)

Workshop Manual
Years: 2004 Manual in English Pages: 150 68.2 MB
Short description

Workshop manual for the Audi A3 (2004) — Electrical system. Includes procedures for battery, starter, alternator, gauges, wipers, exterior/interior lighting and wiring. Edition 02.2018.

199,00 UAH
Contents
Key sections:
  • List of Workshop Manual Repair Groups
  • - 27 Starter, current supply, CCS
  • - 90 Gauges, instruments
  • - 92 Windscreen wash/wipe system
  • - 94 Lights, bulbs, switches - exterior
  • - 96 Lights, bulbs, switches - interior
  • - 97 Wiring
  • 27 - Starter, current supply, CCS
  • 1 Contact corrosion
  • 2 Battery
  • 2.1 Battery - general notes
  • 2.2 Maintenance-free batteries
Buy

Audi A4 / A4 Cabriolet – 4.2 l V8 (5‑valve, timing chains) – Workshop Manual (Mechanics) – Edition 04.2007

Workshop Manual
Years: 2001–2003 Manual in English Pages: 307 7.3 MB
Short description

Comprehensive workshop manual for Audi A4 (2001) and A4 Cabriolet (2003) with the 4.2 L V8, 5‑valve engine with timing chains (Engine IDs BBK/BHF). Includes step‑by‑step procedures for engine removal/installation, crankshaft and timing chain service, cylinder head/valve gear, lubrication, cooling and exhaust system repairs. Intended for professional technicians and service workshops.

199,00 UAH
Contents
Key sections:
  • 00 - Technical data
  • 1 Engine number
  • 2 Engine data (Codes: BBK / BHF; 4.163 l; 253 kW @7000 rpm; torque 410–420 Nm; bore 84.5 mm; stroke 92.8 mm; compression ratio 11.5; RON 98)
  • 3 Safety precautions
  • 4 General repair instructions (cleanliness, fuel system, contact corrosion)
  • 10 - Removing and installing engine
  • 1 Removing engine - vehicles with manual gearbox
  • 1.1 Removing engine (tools, drain fluids, remove bumper, lock carrier, disconnect wiring, fuel, coolant, A/C lines, suspension components, propshaft, exhaust, support engine on platform, lower assembly)
  • 1.2 Separating engine and gearbox (subframe removal, support sets, remove front exhaust pipes, bolt sequence)
  • 1.3 Securing engine to engine and gearbox stand (lifting tackle, VAS 6095 support)
  • 1.4 Installing engine (clutch remarks, alignment, torque values)
  • 2 Removing and installing engine - vehicles with automatic gearbox (procedure parallels manual gearbox with ATF/torque converter notes)
Buy

Audi A4 / A4 Cabriolet — Auxiliary Heater Workshop Manual (Edition 08.2004)

Workshop Manual
Years: 2001 Manual in English Pages: 259 2.0 MB
Short description

Workshop Manual for Audi A4 and A4 Cabriolet — Auxiliary Heater (Edition 08.2004). Contains self-diagnosis procedures, fault tables, electrical and fuel system checks, final control tests, CO₂ exhaust adjustment and step-by-step removal/installation and repair procedures. Intended for professional workshop use.

199,00 UAH
Contents
Key sections:
  • 01 - Self-diagnosis, electrical checks
  • 1 Auxiliary heater self-diagnosis
  • 1.1 Technical data of self-diagnosis
  • 1.2 Function
  • 1.3 Fault recognition
  • 1.4 Guided fault-finding
  • 1.5 Technical data of self-diagnosis
  • 1.6 Test requirements for self-diagnosis
  • 1.7 Safety precautions
  • 2 Self-diagnosis procedure
  • 2.1 Connecting vehicle diagnostic VAS 5051A/K-wire adapter
  • 2.1.1 Control unit identification
Buy

Audi A4 / A4 Cabriolet (1.8T 4‑cyl turbo) — Motronic Injection & Ignition System Service Manual (Edition 01.2015)

Workshop Manual
Years: 2001 Manual in English Pages: 34 851.0 KB
Short description

Service manual for Audi A4 (2001‑) and A4 Cabriolet (2003‑) with 1.8L 4‑cylinder turbo engines. Covers Motronic fuel injection and ignition systems, diagnostic and maintenance procedures. Includes technical data, removal/installation steps and system checks.

199,00 UAH
Contents
Key sections:
  • 24 - Mixture preparation - injection
  • 1 Safety precautions and rules for cleanliness
  • 1.1 General notes on self-diagnosis
  • 1.2 Safety precautions when using testers and measuring instruments during a road test
  • 1.3 Rules for cleanliness and instructions for working on fuel system
  • 1.4 Checking vacuum system
  • 2 Injection system
  • 2.1 Technical data
  • 2.2 Overview of fitting locations - injection system
  • 3 Intake manifold
  • 3.1 Exploded view - intake manifold
  • 3.2 Removing and installing intake manifold
Buy

Audi A8 (2003) — Electrical System Workshop Manual (Edition 08.2014)

Workshop Manual
Years: 2003 Manual in English Pages: 369 9.1 MB
Short description

Comprehensive workshop manual for the Audi A8 (2003) electrical system — Edition 08.2014. Covers battery, alternator, starter, instrument cluster, wiper/washer systems, exterior/interior lighting and wiring repair procedures with step-by-step illustrations. Includes diagnostic and adjustment procedures and torque/data specifications.

199,00 UAH
Contents
Key sections:
  • 27 - Starter, current supply, CCS
  • 1 Contact corrosion
  • 2 Battery
  • 2.1 Battery - general notes
  • 2.2 Maintenance-free batteries
  • 2.3 Disconnecting and connecting battery
  • 2.4 Removing and installing battery
  • - Remove luggage compartment side trim (right-side)
  • - Connect battery charger for back-up power
  • - Detach earth and positive cables, central venting hose
  • - Remove battery retainer plate and lift battery out
  • - Installation notes, adaptation via Vehicle diagnostic tester
Buy

Audi Q4 e-tron (Type F4) - Self-study Programme SSP 685

Workshop Manual
Years: 2021 Manual in English Pages: 186 82.7 MB
Short description

Official Audi Service Training self‑study programme SSP 685 for the Audi Q4 e‑tron (Type F4). Covers body, power units, power transmission, running gear, electrics & electronics, high‑voltage system, thermal management, driver assist and infotainment. Intended for internal service training and technical familiarisation; not a workshop repair manual.

199,00 UAH
Contents
Key sections:
  • Introduction
  • - Introduction to Audi Q4 e-tron
  • - Dimensions
  • Body
  • - Body structure and materials
  • - Joining techniques
  • - Securing high-voltage battery and force progression
  • - Body assembly (doors, rear lid, panoramic sunroof)
  • - Dash panel and centre console
  • Power units
  • - Technical data: rear electric motor (VX90)
  • - Technical data: front electric motor (VX89)
Buy

Audi Q8 (2018) — Electrical System Workshop Manual (Edition 05.2019)

Workshop Manual
Years: 2018 Manual in English Pages: 645 14.8 MB
Short description

Workshop manual for the Audi Q8 (2018) — Electrical System. Includes technical data, safety notes and step‑by‑step repair procedures for battery/charging, starter/alternator, lighting, washer/wiper and wiring. Edition 05.2019.

199,00 UAH
Contents
Key sections:
  • 00 - Technical data
  • 1 Safety precautions
  • 1.1 Safety precautions when working on vehicles with start/stop system
  • 1.2 Safety precautions when using testers and measuring instruments during a road test
  • 1.3 Notes on use and safety for LED headlights and Audi laser lights
  • 2 Repair notes
  • 2.1 Rules for cleanliness
  • 2.2 General notes
  • 2.3 Contact corrosion
  • 2.4 ESD (electrostatic discharge) workplace
  • 2.5 Routing and attachment of lines and wiring
  • 2.6 Identification plates
Buy

Audi Servicing Manual — 7‑Speed Dual Clutch Transmission 0CJ / 0CL / 0CK / 0DN / 0DP / 0HL (Edition 05.2018)

Workshop Manual
Years: 2008–2019 Manual in English Pages: 128 11.1 MB
Short description

Service manual for the 7‑Speed dual‑clutch (DSG) transmissions 0CJ/0CL/0CK/0DN/0DP/0HL fitted to various Audi models. Includes repair information, clutch and gearbox disassembly/assembly, mechatronic and hydraulic system procedures, seals and differential work. Edition 05.2018.

199,00 UAH
Contents
Key sections:
  • 00 - General, Technical Data
  • 1 Repair Information
  • 1.1 General Repair Information
  • 1.2 Contact Corrosion
  • 1.3 ATF Pump, Deactivating and Draining the Hydraulic Pump Reservoir
  • 2 Rules for Cleanliness when Working on DSG® Transmission
  • 30 - Clutch
  • 1 Clutch
  • 1.1 Overview - Flywheel and Dual Clutch
  • 1.2 Flywheel, Removing and Installing
  • 1.3 Dual Clutch, Removing and Installing
  • 1.4 Input Shaft Seal, Replacing
Buy
LAND ROVER 3

Land Rover Defender 300Tdi — Workshop Manual (1996 model year)

Workshop Manual
Defender 300Tdi Years: 1996 Manual in English 7.5 MB
Short description

Official workshop manual for the Land Rover Defender 300Tdi (from 1996 model year). Contains specifications, adjustment, fault diagnosis and step-by-step repair and overhaul procedures for engine, transmission, axles, suspension, brakes, electrical and body. Intended for dealer workshops and trained technicians.

199,00 UAH
Contents
Key sections:
  • 01 INTRODUCTION
  • 04 GENERAL SPECIFICATION DATA
  • 05 ENGINE TUNING DATA
  • 07 GENERAL FITTING REMINDERS
  • 09 LUBRICANTS, FLUIDS AND CAPACITIES
  • 10 MAINTENANCE
  • 12 ENGINE Tdi
  • - Description and operation
  • - Fault diagnosis
  • - Adjustment
  • - Repair and overhaul procedures
  • 19 FUEL SYSTEM Tdi
Buy

Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)

Workshop Manual
Defender Years: 1999–2002 Manual in English 7.6 MB
Short description

Workshop Manual Supplement and Body Repair Manual for the Land Rover Defender. Includes general specifications, maintenance schedules, tuning data and step‑by‑step repair procedures for engine, transmission, suspension, brakes, electrical and body repairs. Covers Defender models from 1999 and 2002 model years.

199,00 UAH
Contents
Key sections:
  • 01 - INTRODUCTION
  • - Introduction
  • - Dimensions
  • - References
  • - Repairs and replacements
  • - Poisonous substances
  • - Fuel handling precautions
  • - Synthetic rubber
  • - Recommended sealants
  • - Used engine oil precautions
  • - Accessories and conversions
  • - Wheels and tyres
Buy

Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)

Workshop Manual
Manual in English Pages: 494 7.1 MB
Short description

Land Rover Range Rover Electrical Library (LRL 0453ENG). Comprehensive manual covering fuse details, earth points, system descriptions, diagnostics and connector pin-outs for electrical troubleshooting and repair. Intended for technicians and service workshops.

199,00 UAH
Contents
Key sections:
  • 1 INTRODUCTION
  • 1.1 About this document
  • 1.2 Battery voltage
  • 1.3 Electrical precautions
  • 1.4 Battery disconnecting / charging
  • 1.5 Disciplines / greases
  • 1.6 Abbreviations
  • 1.7 HeVAC, sensors abbreviations
  • 1.8 How to use this document
  • 1.9 Connector detail format
  • 1.10 Fault diagnosis
  • 1.11 Wire colour codes
Buy
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

Report

Harassment or bullying behavior
Contains mature or sensitive content
Contains misleading or false information
Contains abusive or derogatory content
Contains spam, fake content or potential malware

Block Member?

Please confirm you want to block this member.

You will no longer be able to:

  • See blocked member's posts
  • Mention this member in posts
  • Invite this member to groups
  • Message this member
  • Add this member as a connection

Please note: This action will also remove this member from your connections and send a report to the site admin. Please allow a few minutes for this process to complete.

Report

You have already reported this .