Poor connection or corrosion at the device 6 module connector or at a serial data bus splice pack; Open or chafed serial data wire between the ECM and device 6, often near a harness bend or pass-through; Failed device 6 module, commonly the body control module (BCM) or theft deterrent module depending on the platform; Low battery voltage or a weak battery causing modules to drop offline during cranking; Aftermarket electronics spliced into the serial data bus, such as remote starters or alarms, disturbing bus signals; Faulty ground connection shared by device 6 and other modules on the same circuit; Internal ECM serial data driver fault, though this is less common than wiring or module issues

DTC codes / GM codes / P1606

P1606 · GMSerial Communication Problem With Device 6

Q: What does code P1606 mean?

Serial Communication Problem With Device 6. P1606 on a GM vehicle means the engine control module (ECM) has lost serial data communication with a specific module designated as device 6 on the serial data bus. The ECM sets this code when it expects regular messages from that device and they stop arriving or become corrupted, so the fault is in the communication link or the device itself rather than in the engine management system.

P1606 on a GM vehicle means the engine control module (ECM) has lost serial data communication with a specific module designated as device 6 on the serial data bus. The ECM sets this code when it expects regular messages from that device and they stop arriving or become corrupted, so the fault is in the communication link or the device itself rather than in the engine management system.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyProfessional

AreaComputer and output circuits

Symptoms you may notice

Anti-theft or security warning light illuminated, often with the engine cranking but not starting
Instrument cluster warning messages such as 'Service Theft System' or 'Starting Disabled'
Other modules on the same serial data bus may show communication loss codes or inoperative features
Intermittent no-start condition where the engine may start after several attempts or after the key is cycled
Often no symptoms besides the warning light if the affected device is not critical to engine operation
Radio, climate control, or body functions may behave erratically if device 6 shares a bus segment with those modules

Common causes, most likely first

Poor connection or corrosion at the device 6 module connector or at a serial data bus splice pack
Open or chafed serial data wire between the ECM and device 6, often near a harness bend or pass-through
Failed device 6 module, commonly the body control module (BCM) or theft deterrent module depending on the platform
Low battery voltage or a weak battery causing modules to drop offline during cranking
Aftermarket electronics spliced into the serial data bus, such as remote starters or alarms, disturbing bus signals
Faulty ground connection shared by device 6 and other modules on the same circuit
Internal ECM serial data driver fault, though this is less common than wiring or module issues

How to diagnose and fix it

Verify battery state of charge and perform a voltage drop test on the battery and grounds before condemning any module
Scan all modules for communication codes and record which devices are offline to confirm device 6 is the only missing node
Inspect and clean the device 6 module connector and any serial data bus splice packs for corrosion or loose terminals
Check serial data circuit continuity and resistance from the ECM connector to the device 6 connector, flexing the harness to find intermittent opens
Disconnect aftermarket accessories wired into the serial data bus and retest for the code
Substitute a known-good module of the same part number only after wiring and power/ground checks pass, then reprogram if required
Clear codes and road test through several key cycles to confirm the communication fault does not return

What device 6 really means on a GM bus

Device 6 is not a fixed component across all GM platforms; the same code can point to the body control module, theft deterrent module, or another node depending on the vehicle's serial data architecture, so always check the service information for the specific model.
A weak battery that still cranks the engine can cause modules to brown out during cranking and set P1606 intermittently, which is why voltage and ground testing must come before module replacement.
Aftermarket remote starters and alarm systems spliced into the serial data bus are a frequent cause of this code because they can corrupt bus messages even when the accessory appears to work normally.
The code does not always mean the device 6 module has failed; a single chafed wire or a corroded splice pack terminal can take the whole bus segment down and mimic a dead module.
On some GM vehicles the theft deterrent module is device 6, so a no-start with P1606 should prompt a check of the passlock or passkey system before replacing the ECM.

Can I keep driving with P1606?

If the engine starts and runs normally, the vehicle can be driven to a repair shop, but avoid shutting it off in an unsafe location because a no-start may occur. If the engine cranks but will not start, do not keep cranking; have the vehicle towed to avoid draining the battery and damaging the starter.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.