Weak or failing vehicle battery with low voltage; Corroded or loose battery terminals and ground connections; Blown fuse or faulty wiring in the PCM battery feed circuit; Faulty ignition switch not supplying proper voltage to the PCM; Damaged or shorted CAN bus wiring between PCM and TCM; Failed TCM or PCM internal communication circuit; Aftermarket accessories improperly wired causing voltage drops

DTC codes / GM codes / P1600

P1600 · GMPCM Battery Loss / TCM Communication Loss

Q: What does code P1600 mean?

PCM Battery Loss / TCM Communication Loss. P1600 on GM vehicles indicates that the powertrain control module (PCM) has detected a loss of battery power to its own memory circuit or a communication failure with the transmission control module (TCM). The PCM sets this code when it either loses its keep-alive memory voltage or cannot exchange data with the TCM over the controller area network (CAN) or serial data bus.

P1600 on GM vehicles indicates that the powertrain control module (PCM) has detected a loss of battery power to its own memory circuit or a communication failure with the transmission control module (TCM). The PCM sets this code when it either loses its keep-alive memory voltage or cannot exchange data with the TCM over the controller area network (CAN) or serial data bus.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Illuminated check engine light or service vehicle soon message
Often no symptoms besides the warning light
Transmission may shift harshly or enter limp mode
Engine may crank but not start or stall intermittently
Erratic electrical behavior such as flickering dash lights or radio resets
Loss of stored radio presets or clock reset indicating battery drain

Common causes, most likely first

Weak or failing vehicle battery with low voltage
Corroded or loose battery terminals and ground connections
Blown fuse or faulty wiring in the PCM battery feed circuit
Faulty ignition switch not supplying proper voltage to the PCM
Damaged or shorted CAN bus wiring between PCM and TCM
Failed TCM or PCM internal communication circuit
Aftermarket accessories improperly wired causing voltage drops

How to diagnose and fix it

Perform a battery load test and replace if voltage drops below 9.6 volts during cranking
Clean and tighten all battery terminals and engine ground straps
Check all fuses related to the PCM and TCM power circuits
Measure voltage at the PCM battery feed terminal with key off and key on
Inspect CAN bus wiring for chafing, corrosion, or loose connectors between PCM and TCM
Use a scan tool to check for communication with the TCM and perform a bidirectional test if possible
If all wiring and power checks pass, substitute a known-good TCM or PCM for testing

When P1600 is not a dead PCM

A weak battery that still starts the engine can set P1600 because the PCM sees a voltage dip during cranking that drops below its memory threshold.
Corroded ground connections on the engine block or chassis often mimic a failed PCM and are frequently overlooked during diagnosis.
Aftermarket remote starters or alarm systems tapped into the ignition circuit can cause intermittent voltage drops that set P1600 without any hard fault.
The TCM on many GM models is internal to the transmission and a communication loss can be caused by a failing transmission harness rather than the module itself.
P1600 can be stored as a history code after a battery replacement or jump start and may not indicate an active fault if the light is off.

Can I keep driving with P1600?

If the check engine light is on but the vehicle runs and shifts normally, you can drive cautiously to a repair shop, but avoid long trips and heavy electrical loads. If the transmission is in limp mode or the engine stalls, stop driving and have the vehicle towed to prevent damage.

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.