Experiencing intermittent issues with your VW Jetta ALH TDI where the ECU seems to be failing to communicate? You’re not alone. Many Jetta owners have encountered frustrating situations where their car sporadically refuses to start, accompanied by a confusing array of warning lights and diagnostic communication failures. This article delves into diagnosing these ECU communication problems, particularly in Jetta ALH models, and explores potential connections to car alarm or security system malfunctions.
The owner of a Jetta TDI recently reached out for assistance in online forums, detailing a perplexing issue of intermittent ECU communication. Like many others, they initially faced difficulty even connecting diagnostic tools to their vehicle. Let’s examine the symptoms and troubleshooting steps taken in this real-world scenario, and how they might relate to the broader topic of ECU and car alarm problems in Jetta ALH vehicles.
Symptoms of ECU Communication Failure in Jetta ALH
The primary symptom described was the Jetta’s ECU intermittently failing to “chat back,” meaning it wouldn’t communicate with diagnostic tools. This was observed with multiple OBD readers, from basic to more advanced, including the VCDS (VAG-COM Diagnostic System). This lack of communication was coupled with inconsistent starting behavior.
Here’s a breakdown of the key symptoms:
- Intermittent No-Start Condition: The car would sometimes crank but not start.
- Warning Light Behavior: When the car did start, the engine light, steering light, and airbag light would illuminate. Conversely, when it wouldn’t start, none of these lights would appear when the key was turned to the “On” position.
- Diagnostic Tool Failure: Multiple OBD readers and VCDS failed to establish communication with the ECU during the no-start condition.
This on-again, off-again nature of the problem points towards an intermittent electrical issue affecting the ECU’s ability to function and communicate.
Initial Investigation: Environmental Factors
The car owner, in their forum post, described a crucial initial finding: a damp ECU. Upon inspecting the ECU location, they discovered it was “smothered in insulation” and wet, likely due to a critter infestation and recent rain. This highlights the importance of physically inspecting the ECU and its surrounding environment when diagnosing communication issues, especially in older vehicles where seals and protective measures may have degraded.
Alt text: Location of the Engine Control Unit (ECU) in a VW Jetta, often found under the hood near the windshield or in the engine bay.
Cleaning and drying the ECU and its connectors seemed to temporarily resolve the problem. The Jetta ran without issue for about a month, even in wet conditions. However, the problem recurred, indicating that while moisture may have been a contributing factor, it wasn’t the sole root cause. This is a common scenario in automotive diagnostics – addressing one symptom may not fix the underlying problem.
Recurring Symptoms and Deeper Dive
When the issue returned, the 50/50 start probability became more apparent. The correlation between the engine light (and other associated lights) and the car starting became a key diagnostic clue. If the lights illuminated upon turning the key, the car would start and run normally. If the lights remained off, the car would crank but not start.
The fact that the engine cranks is an important distinction. It suggests the starter motor and battery are functioning, but the engine isn’t receiving the necessary signals to initiate combustion. This further points towards a problem with engine management, likely stemming from the ECU or related components.
Troubleshooting Steps and VCDS Scan
To further diagnose the issue, the car owner performed several troubleshooting steps:
- Fuse Check: The ECU communication fuse was checked and even replaced, although voltage at the fuse indicated it was likely not the problem.
- Engine Control Relay Inspection: The Engine Control Relay was tested on a bench with a 12V source and appeared to function correctly. Its removal, however, resulted in a no-crank condition, reinforcing its role in engine starting and highlighting the difference in symptoms compared to the intermittent ECU communication issue.
- Wiring Harness Inspection: A visual inspection of the wiring harness was conducted, looking for obvious signs of damage like chewing or chafing, but no issues were immediately apparent without removing protective wrappings.
Despite these checks, the intermittent problem persisted. A VCDS scan was performed when the engine light was not illuminated (during a no-communication/no-start event). The scan report revealed a multitude of communication errors across various modules.
Sunday,08,January,2023,14:23:47:09323
VCDS -- Windows Based VAG/VAS Emulator
Running on Windows 10 x64
VCDS Version: 22.3.1.4 (x64)
HEX-V2 CB: 0.4615.4 Data version: 20220407 DS337.0
www.Ross-Tech.com
VIN: 3VWRL71KX9M027009
License Plate:
Mileage: 334510km-207854mi Repair Order:
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
Chassis Type: 1K (1K0)
Scan: 01 03 08 09 0F 15 16 17 19 1C 25 42 44 46 52 56 62 65 72
VIN: 3VWRL71KX9M027009 Mileage: 334510km-207854miles
01-Engine -- Status: Sporadic communication error 1000
03-ABS Brakes -- Status: Malfunction 0010
04-Steering Angle -- Status: OK 0000
08-Auto HVAC -- Status: Malfunction 0010
09-Cent. Elect. -- Status: Malfunction 0010
0F-Digital Radio -- Status: Malfunction 0010
15-Airbags -- Status: OK 0000
16-Steering wheel -- Status: Malfunction 0010
17-Instruments -- Status: Malfunction 0010
19-CAN Gateway -- Status: Malfunction 0010
1C-Position Sensing -- Status: OK 0000
25-Immobilizer -- Status: OK 0000
42-Door Elect, Driver -- Status: Malfunction 0010
44-Steering Assist -- Status: Malfunction 0010
46-Central Conv. -- Status: OK 0000
52-Door Elect, Pass. -- Status: OK 0000
56-Radio -- Status: Malfunction 0010
62-Door, Rear Left -- Status: OK 0000
65-Tire Pressure -- Status: OK 0000
72-Door, Rear Right -- Status: OK 0000
-------------------------------------------------------------------------------
Address 01: Engine (CBE) Labels: 03L-906-022-CBE.clb
Part No SW: 03L 997 016 N HW: 03L 906 022 J
Component: R4 2,0L EDC G000SG 9970 Revision: 12H01---
Serial number: VWX7Z0H524U12F Coding: 0050072
Shop #: WSC 01824 002 1048576 VCID: 3D2734DA2173E853E49-8068
VINID: 0E69E270705BA097400870002418029DDF
No fault code found.
Readiness: 0 0 0 0 0
-------------------------------------------------------------------------------
Address 03: ABS Brakes (-----) Labels:. 1K0-907-379-60EC1F.clb
Part No SW: 1K0 907 379 AN HW: 1K0 907 379 AN
Component: ESP MK60EC1 H45 0107 Revision: 00H45001
Coding: 113B400D49240001880B02E4922200423000 Shop #: WSC 39780 001 1048576 VCID: 7EA5F3D660F5334BBD3-802A
1 Fault Found:
01314 - Engine Control Module
004 - No Signal/Communication - Intermittent
Freeze Frame:
Fault Status: 00100100
Fault Priority: 2
Fault Frequency: 1
Reset counter: 193
Mileage: 334512 km
Time Indication: 0
Freeze Frame:
Count: 0
Count: 2
Count: 4608
Count: 8194
Count: 42752
Count: 0
Count: 0
Count: 0
-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: 1K0-820-047.lbl
Part No SW: 1K0 820 047 HS HW: 1K0 820 047 HS
Component: Climatic PQ35 142 1111 Revision: 00142031
Serial number: 00000000000000 Shop #: WSC 00000 000 00000 VCID: 7CA1F9DE7AE9215B937-8028
1 Fault Found:
01314 - Engine Control Module
004 - No Signal/Communication - Intermittent
-------------------------------------------------------------------------------
Address 09: Cent. Elect. Labels:. 3C0-937-049-30-M.lbl
Part No SW: 3C8 937 049 D HW: 3C8 937 049 D
Component: Bordnetz-SG H54 2602 Revision: 00H54000
Serial number: 00000001027669 Coding: 14018E234004150007140000001400000008730B5C000120000000000000
Shop #: WSC 00066 000 00000 VCID: 323D17E6E82D272B09B-8066
Subsystem 1 - Part No: 1K1 955 119 E Labels: 1KX-955-119.CLB
Component: Wischer 050808 021 0501 Coding: 00038805
Shop #: WSC 00066
1 Fault Found:
01314 - Engine Control Module
004 - No Signal/Communication - Intermittent
Freeze Frame:
Fault Status: 00100100
Fault Priority: 6
Fault Frequency: 4
Reset counter: 233
Mileage: 334512 km
Time Indication: 0
Freeze Frame:
ON
Voltage: 12.05 V
ON
ON
OFF
OFF
OFF
-------------------------------------------------------------------------------
Address 0F: Digital Radio Labels: 8E0-035-593-SIR.lbl
Part No SW: 8E0 035 593 M HW: 8E0 035 593 M
Component: SDAR SIRIUS H07 0150 Revision: 00000000
Serial number: AUZ4Z7H0377980 Coding: 0000100
Shop #: WSC 00066 000 00000 VCID: 333312E217372E2302D-8066
1 Fault Found:
02635 - Tuner Not Enabled/Activated
000 - -
Freeze Frame:
Fault Status: 01100000
Fault Priority: 7
Fault Frequency: 1
Reset counter: 179
Mileage: 333879 km
Time Indication: 0
Date: 2000.00.00
Time: 14:34:47
-------------------------------------------------------------------------------
Address 15: Airbags Labels: 1K0-909-605.lbl
Part No SW: 1K0 909 605 AB HW: 1K0 909 605 AB
Component: 6A AIRBAG VW8R 034 8000 Revision: 05034000
Serial number: 003B6M068Z05 Coding: 0013889
Shop #: WSC 00066 000 00000 VCID: 6C81C99E0A89B1DB037-8038
Subsystem 1 - Part No: 1K0 959 339 H Component: BF-Gewichtsens. 007 0006
Subsystem 2 - Serial number: 6332MSME3D70393CL
Subsystem 3 - Serial number: 6342MSME2F61537FQ
Subsystem 4 - Serial number: 6351HSME166347688
Subsystem 5 - Serial number: 6361HSME17191230Z
Subsystem 6 - Serial number: 63727SME16705F32%
Subsystem 7 - Serial number: 63827SME16705230S
No fault code found.
-------------------------------------------------------------------------------
Address 16: Steering wheel Labels: 1K0-953-549-MY8.lbl
Part No SW: 1K0 953 549 BS HW: 1K0 953 549 BS
Component: J0527 051 0101 Coding: 0002021
Shop #: WSC 00066 000 00000 VCID: 0451813E0219599BEB7-8050
Subsystem 1 - Part No: XXXXXXXXXXX Component: E0221 002 0010
5 Faults Found:
00576 - Terminal 15
012 - Electrical Fault in Circuit - Intermittent
00883 - Ignition Switch (D) Terminal S
012 - Electrical Fault in Circuit - Intermittent
00884 - Ignition Switch (D) Terminal X
012 - Electrical Fault in Circuit - Intermittent
01744 - Ignition Switch Terminal P (D)
012 - Electrical Fault in Circuit - Intermittent
00885 - Ignition Switch (D) Terminal 50
012 - Electrical Fault in Circuit - Intermittent
-------------------------------------------------------------------------------
Address 17: Instruments Labels: 1K0-920-xxx-17.lbl
Part No SW: 1K0 920 974 N HW: 1K0 920 974 N
Component: KOMBIINSTRUMENT 3HL 2418 Revision: V0003000
Serial number: VWX7Z0H524U12F Coding: 0023203
Shop #: WSC 25019 444 67490 VCID: 392F20CA355BD473C81-806C
1 Fault Found:
01314 - Engine Control Module
004 - No Signal/Communication - Intermittent
Freeze Frame:
Fault Status: 00100100
Fault Priority: 2
Fault Frequency: 24
Reset counter: 233
Mileage: 334512 km
Time Indication: 0
Date: 2000.00.00
Time: 05:14:15
-------------------------------------------------------------------------------
Address 19: CAN Gateway Labels:. 1K0-907-530-V3.clb
Part No SW: 1K0 907 530 Q HW: 1K0 907 951
Component: J533 Gateway H07 0062 Revision: H07 01
Serial number: 160608F1000231 Coding: E9807F070013021002
Shop #: WSC 00066 000 00000 VCID: 35372CFA194330132C9-8060
1 Fault Found:
01314 - Engine Control Module
004 - No Signal/Communication - Intermittent
Freeze Frame:
Fault Status: 00100100
Fault Priority: 2
Fault Frequency: 9
Reset counter: 233
Mileage: 333988 km
Time Indication: 0
Date: 2000.00.00
Time: 18:59:15
-------------------------------------------------------------------------------
Address 1C: Position Sensing Labels: 1Kx-919-xxx-1C.lbl
Part No SW: 1K5 919 965 A HW: 1K5 919 965 A
Component: Kompass 005 0004 Revision: 00005000
Serial number: 1293324T327B04 Coding: 0000003
Shop #: WSC 00066 000 00000 VCID: 392F20CA355BD473C81-806C
No fault code found.
-------------------------------------------------------------------------------
Address 25: Immobilizer Labels: 1K0-920-xxx-25.clb
Part No SW: 1K0 920 974 N HW: 1K0 920 974 N
Component: IMMO 3HL 2418 Revision: V0003000
Serial number: VWX7Z0H524U12F Shop #: WSC 00000 000 00000 VCID: 392F20CA355BD473C81-806C
No fault code found.
-------------------------------------------------------------------------------
Address 42: Door Elect, Driver Labels:. 1K0-959-701-MIN3.clb
Part No SW: 1K0 959 701 AC HW: 1K0 959 793 N
Component: J386 TUER-SG FT 1519 Revision: 72009005
Serial number: 00000070788710 Coding: 0001205
Shop #: WSC 00066 000 00000 VCID: 6FBBDE923B9F4AC3265-803A
2 Faults Found:
01552 - Motor for Central Locking; Drivers Door (V56); Lock
012 - Electrical Fault in Circuit - Intermittent
Freeze Frame:
Fault Status: 00101100
Fault Priority: 3
Fault Frequency: 51
Reset counter: 233
Mileage: 334238 km
Time Indication: 0
00928 - Locking Module for Central Locking; Front Driver Side (F220)
008 - Implausible Signal - Intermittent
Freeze Frame:
Fault Status: 00111000
Fault Priority: 3
Fault Frequency: 24
Reset counter: 233
Mileage: 334326 km
Time Indication: 0
-------------------------------------------------------------------------------
Address 44: Steering Assist Labels: 1K0-909-14x-GEN3.clb
Part No: 1K0 909 144 C Component: EPS_ZFLS Kl. 70 2301
Revision: 00H15000 Shop #: WSC 02069 000 90108 VCID: 2A0D0F86C0FD6FEBB1B-807E
2 Faults Found:
00750 - Warning Lamp
013 - Check DTC Memory - Intermittent
Freeze Frame:
Fault Status: 00101101
Fault Priority: 2
Fault Frequency: 2
Reset counter: 50
Mileage: 334512 km
Time Indication: 0
Date: 2000.00.00
Time: 12:28:04
Freeze Frame:
Voltage: 12.00 V
DU Temperature: 13.0°C
RPM: 0 /min
Speed: 0.0 km/h
Speed: 0.0 km/h
Count: 0
01314 - Engine Control Module
004 - No Signal/Communication - Intermittent
Freeze Frame:
Fault Status: 00100100
Fault Priority: 3
Fault Frequency: 4
Reset counter: 243
Mileage: 334512 km
Time Indication: 0
Date: 2000.00.00
Time: 12:27:58
Freeze Frame:
Voltage: 12.00 V
DU Temperature: 13.0°C
RPM: 1498 /min
Speed: 0.0 km/h
Speed: 0.0 km/h
Count: 0
-------------------------------------------------------------------------------
Address 46: Central Conv. Labels:. 1K0-959-433-MAX.clb
Part No SW: 1K0 959 433 CT HW: 1K0 959 433 CT
Component: KSG PQ35 RDK 052 0221 Revision: 00052000
Serial number: 00000000000000 Coding: 13900F880186281B0904058FB0880F0488DC00
Shop #: WSC 00066 000 00000 VCID: 0451813E0219599BEB7-8050
Subsystem 1 - Component: Sounder n.mounted
Subsystem 2 - Component: NGS n.mounted
Subsystem 3 - Component: IRUE n.mounted
No fault code found.
-------------------------------------------------------------------------------
Address 52: Door Elect, Pass. Labels:. 1K0-959-702-MIN3.clb
Part No SW: 1K0 959 702 AC HW: 1K0 959 792 N
Component: J387 TUER-SG BT 1519 Revision: 72009005
Serial number: 00000076888726 Coding: 0001204
Shop #: WSC 00066 000 00000 VCID: 70B9DDEE26A1553B3FF-8024
No fault code found.
-------------------------------------------------------------------------------
Address 56: Radio Labels: 1K0-035-1xx-56.clb
Part No SW: 1K0 035 180 L HW: 1K0 035 180 L
Component: Radio DE2 016 0020 Revision: 00016000
Serial number: VWZ4Z7H2220398 Coding: 0010400
Shop #: WSC 00000 000 00000 VCID: 290FF08AC5FB64F3B81-807C
2 Faults Found:
01044 - Control Module Incorrectly Coded
000 - -
00003 - Control Module
014 - Defective
-------------------------------------------------------------------------------
Address 62: Door, Rear Left Labels:. 1K0-959-703-GEN3.clb
Part No SW: 1K0 959 703 AH HW: 1K0 959 795 T
Component: J388 TUER-SG HL 1401 Revision: 12006001
Serial number: 00000003285375 Coding: 0001168
Shop #: WSC 00066 000 00000 VCID: 76B5EBF644C57B0BE53-8022
No fault code found.
-------------------------------------------------------------------------------
Address 65: Tire Pressure Labels: 3C0-959-433-65.lbl
Part No SW: 1K0 959 433 CT HW: 1K0 959 433 CT
Component: RDK 0450 Revision: 00052000
Serial number: 00000000000000 Coding: 0100101
Shop #: WSC 00066 000 00000 VCID: 0451813E0219599BEB7-8050
No fault code found.
-------------------------------------------------------------------------------
Address 72: Door, Rear Right Labels:. 1K0-959-704-GEN3.clb
Part No SW: 1K0 959 704 AH HW: 1K0 959 794 T
Component: J389 TUER-SG HR 1401 Revision: 12006001
Serial number: 00000003342350 Coding: 0001168
Shop #: WSC 00066 000 00000 VCID: 77ABE6F243CF0203FE5-8022
No fault code found.
End----------(Elapsed Time: 01:29, VBatt start/end: 12.2V/12.2V)-----------Analyzing the VCDS Scan Report
The VCDS scan report is revealing. Notably, the Engine module (Address 01) itself reports “Sporadic communication error” but “No fault code found.” However, numerous other modules, including ABS Brakes, Auto HVAC, Central Elect., Digital Radio, Steering wheel, Instruments, CAN Gateway, Steering Assist, and Radio, all log “01314 – Engine Control Module: No Signal/Communication – Intermittent” fault codes.
Alt text: Screenshot of a VCDS scan tool interface displaying multiple fault codes related to ECU communication issues in a VW Jetta.
This widespread communication failure, originating from the Engine Control Module, is the central issue. Furthermore, the Steering Wheel module (Address 16) shows multiple “Electrical Fault in Circuit – Intermittent” faults related to the ignition switch terminals (Terminal 15, S, X, P, 50). These ignition switch faults could be critical, as the ignition switch provides power and signals to the ECU and other systems.
Potential Causes and Next Steps
Based on the symptoms, troubleshooting, and VCDS scan, several potential causes emerge:
- Faulty ECU: The ECU itself could be failing intermittently due to internal component issues, potentially exacerbated by moisture exposure.
- Wiring Harness Problem: Despite the initial visual inspection, there could be a break, corrosion, or intermittent short in the wiring harness leading to the ECU, particularly in power or ground wires, or the CAN bus communication lines. The critter infestation could have damaged wiring beneath the surface.
- Ignition Switch Malfunction: The multiple ignition switch fault codes suggest a potential problem with the ignition switch itself. A failing ignition switch could intermittently interrupt power or signals to the ECU and other modules.
- Immobilizer System (Less Likely): While the Immobilizer module (Address 25) shows no fault codes, immobilizer issues can sometimes manifest in no-start conditions. However, the consistent communication errors across multiple modules make a general ECU communication problem more probable.
Connecting to “Car Alarm” and Security Systems: While not directly related to a traditional car alarm siren, ECU and electrical system malfunctions can indirectly affect car security systems. For example, a faulty ECU or ignition switch could potentially trigger false alarms or cause erratic behavior in systems that rely on ECU signals. Furthermore, immobilizer issues, which are part of the car’s anti-theft system, are intertwined with the ECU. While the scan shows no immobilizer faults, a deeper investigation might reveal subtle interactions. In a broader sense, electrical gremlins causing ECU communication problems can certainly compromise the overall reliability and security of the vehicle.
Recommended Next Steps:
- Detailed Wiring Harness Inspection: A thorough inspection of the ECU wiring harness is crucial. This should involve removing protective wrappings and checking for continuity, shorts, and corrosion, especially at connectors. Focus on power and ground wires to the ECU and the CAN bus wires.
- Ignition Switch Test/Replacement: Given the ignition switch fault codes, testing or replacing the ignition switch should be considered.
- ECU Removal and Bench Test/Replacement: If wiring and ignition switch are ruled out, the ECU itself may be the culprit. Consider removing the ECU and inspecting connectors for corrosion or damage. A specialized shop may be able to bench test the ECU. Replacement might be necessary.
- Professional Diagnostic Assistance: Due to the complexity of intermittent electrical issues, seeking professional help from a qualified VW technician with experience in diagnosing ECU and electrical system problems is highly recommended.
Diagnosing intermittent ECU communication issues in Jetta ALH TDI models requires a systematic approach, combining symptom analysis, diagnostic scans, and thorough physical inspections. While the term “car alarm” in the keyword might seem tangential, understanding the broader implications of ECU and electrical system health on vehicle security and reliability is essential. By following a logical troubleshooting process, and potentially seeking professional help, Jetta owners can effectively address these frustrating problems and get back on the road with confidence.
