P1615

Code

GMC P — Powertrain

Loss Of VTD Serial Data

Brand: GMC

Type: P — Powertrain

Views: UK: 36 EN: 57 RU: 28

AI status

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Page language: EN

Causes

Open or short in serial data wiring (Class 2/GMLAN)
Faulty or unpowered VTD (Vehicle Theft Deterrent) module
Faulty Body Control Module (BCM) or PCM/ECM communication circuits
Blown fuse or poor battery/ignition power to VTD or related modules
Intermittent connector or pin corrosion
Aftermarket alarm/remote start or improper installation interfering with data bus

Symptoms

Security/anti-theft or “Service Theft System” lamp illuminated or flashing
Engine cranks but will not start, or crank no-start condition
Remote key fob/keyless entry functions inoperative or intermittent
Loss of functions controlled by VTD messages (instrument cluster warnings, remote start disabled)
Set manufacturer-specific DTC P1615 and possibly other communication U-codes

What to check

Use a capable scan tool to read freeze frame and stored codes from all modules (BCM, IPC, ECM, VTD if available)
Verify battery voltage is within specification (check while cranking)
Inspect fuses and power/ground circuits for the VTD, BCM and related modules
Visually inspect connectors and wiring for damage, corrosion, or aftermarket splices near the VTD and BCM
Check for other communication codes (U-codes) that indicate a broader bus problem
With the scan tool observe serial data activity (module list and live data) to confirm whether the VTD appears on the network

Signal parameters

Healthy serial data bus shows regular packet activity and no constant voltage (digital waveform pulses rather than a fixed DC level)
No short to battery or ground on the serial data line; no bus contention (multiple drivers holding line)
Power and ground to VTD should be stable and within battery/ignition supply limits while key is on or cranking
Related module presence: VTD ID and expected messages should appear intermittently during wake-up and continuously when active

Diagnostic algorithm

Read all stored and pending DTCs in all modules; note any U-codes indicating larger bus faults.
Verify battery condition and measure key-on voltage at a battery and module ground. Repair battery/charging issues first.
Inspect fuses and relay related to VTD/BCM power and replace if blown. Verify ignition-switched power present at VTD connector when key on.
Visually inspect VTD and BCM connectors and harness routing for damage, corrosion or aftermarket splices; repair any damage and make secure ground connections.
Using a scan tool, check if the VTD module is present on the network and if it is sending/receiving messages. If the VTD does not appear, proceed to wiring checks.
Back-probe the serial data line at the VTD connector and look for packet activity with a scope or a serial-data capable scan tool. Check for shorts to battery or ground.
If wiring checks good but no communication from VTD, verify power/ground at the VTD pins; if power/ground present and no comms, suspect VTD internal fault—attempt module wake-up or replacement as directed by service manual.
Check for and disconnect any aftermarket alarm or remote start unit; re-test communications.
If modules have recently been replaced or reprogrammed, confirm correct software levels and perform required module programming/relearn procedures.
Clear codes and perform test drive/monitor to confirm repair. If intermittent, perform wiggle-testing of harness while monitoring serial bus for faults.

Likely causes

Damaged or disconnected data-bus harness at VTD or BCM
Blown fuse supplying VTD module or BCM power/ignition feed
Faulty VTD module not transmitting serial packets
Corroded connector pins at VTD or a ground circuit fault
Aftermarket device placed on the same bus causing bus contention

Fault status

⚠️ Status

P1615 — Loss of VTD serial data: the Vehicle Theft Deterrent (VTD) module is not communicating on the vehicle serial data bus; may cause immobilizer/no-start and security lamp.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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