Damaged, corroded or loose wiring and connectors in the serial data circuit between the PCM and ABS module; Poor ground connection at the ABS module or PCM mounting points; Failed ABS control module, often from internal circuit board faults or water intrusion; Failed or intermittent PCM communication driver; Blown fuse or poor power feed to the ABS module; Aftermarket electronics or poor previous repairs disturbing the data bus wiring

DTC codes / GM codes / P1602

P1602 · GMPCM to ABS Module Communication Problem

Q: What does code P1602 mean?

PCM to ABS Module Communication Problem. P1602 on a GM vehicle means the powertrain control module (PCM) has lost or detected a fault in its serial data communication link with the anti-lock brake system (ABS) module. The PCM sets this code when it cannot reliably exchange messages with the ABS controller over the vehicle's data bus, so it flags the communication circuit rather than a brake hydraulic fault.

P1602 on a GM vehicle means the powertrain control module (PCM) has lost or detected a fault in its serial data communication link with the anti-lock brake system (ABS) module. The PCM sets this code when it cannot reliably exchange messages with the ABS controller over the vehicle's data bus, so it flags the communication circuit rather than a brake hydraulic fault.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyProfessional

AreaComputer and output circuits

Symptoms you may notice

Anti-lock brake warning light illuminated on the dashboard
Traction control or stability control warning light also on, since those functions rely on the ABS module
Speedometer may read erratically or drop to zero if wheel speed data is lost
ABS and traction control systems disabled, with normal braking still available
Often no symptoms besides the warning light, with the vehicle driving normally
Intermittent warning lights that come and go over bumps or in wet weather

Common causes, most likely first

Damaged, corroded or loose wiring and connectors in the serial data circuit between the PCM and ABS module
Poor ground connection at the ABS module or PCM mounting points
Failed ABS control module, often from internal circuit board faults or water intrusion
Failed or intermittent PCM communication driver
Blown fuse or poor power feed to the ABS module
Aftermarket electronics or poor previous repairs disturbing the data bus wiring

How to diagnose and fix it

Scan all modules for codes and record which modules are communicating before clearing anything
Inspect the ABS module connectors and PCM connectors for corrosion, pushed pins or loose terminals
Check the ABS module power and ground circuits with a multimeter under load
Perform a voltage drop test on the data bus wiring between the PCM and ABS module
Check for technical service bulletins on the data bus and ABS module for the specific GM model
Substitute a known-good ABS module only after wiring and power checks pass
Clear codes and verify communication with a bidirectional scan tool over several drive cycles

What the data bus fault really means

A P1602 is frequently caused by a chafed or corroded wire in the wheel well or engine bay harness rather than a failed ABS module, so inspect the harness routing before condemning parts.
The code can be set by a weak battery or charging system, because low voltage during cranking disrupts module communication and logs false communication faults.
Aftermarket alarms, remote starters or audio installs tapped into the data bus are a common hidden cause on older GM trucks and SUVs.
A failed ABS module can still allow normal braking, so drivers often ignore the light until inspection time, but traction control and stability assist are unavailable while the code is active.
Clearing the code without repairing the circuit often results in the light returning after a few drive cycles once the module handshake fails again.

Can I keep driving with P1602?

The vehicle remains safe to drive with normal brakes because the ABS module fault does not affect hydraulic braking, but you should avoid relying on anti-lock or traction control and get the circuit inspected soon. Do not tow or drive aggressively in low-traction conditions until the communication fault is repaired.

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.