P2DA1

Code

Generic P — Powertrain

Gear Shift Control Module B Supply Voltage Low

Brand: Generic

Type: P — Powertrain

Views: UK: 19 EN: 32 RU: 26

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Page language: EN

Causes

Weak or discharged battery
Faulty or undercharging alternator/voltage regulator
Blown fuse or fusible link in GSCM-B supply circuit
Open or high-resistance power wiring to the module
Poor or corroded ground(s) at the module or chassis
Damaged/shorted connector or wiring harness (short to ground)

Symptoms

Transmission or gear selector warning lamp illuminated
Transmission shifts intermittently or fails to shift
Stored/active DTC(s) related to GSCM-B supply or communication
Loss of some shift functions or limp/home mode engaged
Erratic or delayed gear selection
Symptoms may be intermittent or present only when electrical load is high

What to check

Read and record all stored DTCs and freeze-frame data
Visually inspect battery terminals, ground straps, engine/chassis grounds, and connectors for corrosion or looseness
Check fuses and fusible links related to transmission/GSCM-B supply
Measure battery resting voltage and voltage with engine running (charging system check)
Backprobe GSCM-B supply pin with key ON (engine off) and with engine running; compare to battery voltage
Check continuity/resistance of power feed and ground circuits between battery and module

Signal parameters

Battery voltage (engine off, resting): ~12.2–12.8 V typical
Battery voltage (key ON, engine off): ~11.5–13.0 V; should be close to battery voltage with ignition ON
Charging system (engine running): ~13.5–14.8 V
Module supply pin: should be within ~0.2–0.5 V of battery/ignition feed under no-load conditions
Ground circuit resistance:
Supply current draw for module in normal sleep/idle: typically small (hundreds of mA or less) — manufacturer-specific

Diagnostic algorithm

Capture and save DTCs/freeze-frame, then clear codes and attempt to re-create fault.
Measure and record battery voltage (resting) and while cranking; ensure battery state is good. Charge or replace if low.
Verify charging system output at battery with engine running (13.5–14.8 V). Repair alternator/regulator if out of range.
Inspect and test all fuses, fusible links and relays supplying GSCM-B; replace any blown or corroded items.
Backprobe the GSCM-B supply pin(s) with key ON and engine running; compare to battery/ignition rail. Note any voltage drop under load.
Inspect connector pins for corrosion, bent pins, or loose terminals; repair and reseal as required.
Check continuity and resistance of the power feed and ground conductors between the battery and module. Repair any high-resistance joints.
Perform wiggle testing of harness while monitoring voltage and module behavior to find intermittent opens/shorts.
If low voltage persists with wiring and charging system good, check upstream ignition switch/relay circuits for correct operation.
If wiring and supply are confirmed good and no parasitic faults found, suspect module internal failure—refer to manufacturer for module bench test or replacement procedures.
After repairs, clear DTCs, confirm proper voltages, and road-test to verify the fault does not return.

Likely causes

Blown fuse or poor fuse/relay contact to GSCM-B
Corroded or loose ground at module or nearby chassis ground
Damaged power feed or connector (chafed wire, water intrusion)
Weak battery or failing alternator not maintaining voltage under load
Failed GSCM-B (less likely after wiring and power verified)

Fault status

⚠️ Status

GSCM-B supply voltage below threshold — module supply circuit is low or intermittent. Check battery, charging system, protection devices, wiring and grounds.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours