P1600

Code

VOLKSWAGEN P — Powertrain

Power Supply Terminal No 15 Low Voltage

Brand: VOLKSWAGEN

Type: P — Powertrain

Views: UK: 36 EN: 59 RU: 42

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Page language: EN

Causes

Weak or discharged battery
Poor battery positive or negative connections (corrosion, loose terminals)
Faulty ignition switch or ignition/starter relay
Blown or corroded fuse in the Terminal 15 circuit
High-resistance wiring or connector damage in the Terminal 15 feed (open, partial short to ground)
Faulty alternator or charging system causing overall low system voltage

Symptoms

Multiple warning lights or instrument cluster warnings when key ON
Engine cranks slowly or no-crank/no-start condition
Engine stalls or runs intermittently
Loss of communication with control modules (CAN/bus errors)
Reduced performance or limp-home mode triggered
Accessories fail or behave erratically with ignition ON

What to check

Read and record all stored DTCs and freeze-frame data with a capable scanner
Visually inspect battery terminals, cables, fusebox, ignition switch and related wiring for corrosion or damage
Measure battery resting voltage (key OFF) with a multimeter
Measure voltage at Terminal 15 (fuse or ECU connector that is fed by ignition switch) with key in ON (engine OFF)
Measure voltage at Terminal 15 while cranking and compare to battery voltage to check for excessive voltage drop
Perform a voltage drop test between battery positive and Terminal 15 under load (should be minimal)

Signal parameters

Battery resting voltage (key OFF): ~12.4–12.8 V expected for healthy battery
Key ON (engine OFF) Terminal 15 voltage: should be approximately battery voltage (typically ~12–14.5 V)
While cranking Terminal 15: voltage may drop but normally stays above ~9 V on healthy battery/starting system (manufacturer limits vary)
Acceptable voltage drop between battery positive and Terminal 15 under load: typically
Ground circuit resistance: very low (ideally

Diagnostic algorithm

Capture and save DTCs and any freeze-frame data using a full-function scan tool. Note when the fault was logged (key on/cranking/driving).
Visually inspect battery posts, cable ends, engine/chassis grounds, fusebox and connectors for corrosion, looseness or damage. Clean and tighten as required.
Measure and record battery voltage with key OFF. If battery
With key ON (engine OFF), measure voltage at the battery positive and at the Terminal 15 feed point (fuse, relay output, or ECU connector). Compare readings—voltage at Terminal 15 should be within a few tenths of battery voltage.
Perform a voltage drop test between battery positive terminal and Terminal 15 while trying to start (or under comparable load). Voltage drop >0.5 V suggests high resistance in the feed (bad connector, wiring, relay, fuse).
Check/replace fuses and test ignition relay operation. Bypass or bench-test relay if suspect.
Inspect wiring harness and connector pins at ECU, fusebox and ignition switch for damage or corrosion. Wiggle-test while monitoring voltage for intermittent faults.
Test charging system (alternator) output with engine running once starting is successful or after battery charged. Verify system charging voltage ~13.5–14.8 V.
If wiring, connectors, fuses, relays and battery/alternator are good, consider ignition switch replacement or further module-level testing. If a module is suspected of internal shorting, follow manufacturer module diagnostics; replace only after confirming.
Clear codes and perform a road test to confirm repair; rescan to ensure P1600 does not reappear.

Likely causes

Battery state of charge low or battery failing
Loose/corroded battery terminals or engine/chassis ground
Faulty ignition switch or failing ignition relay contacts
Blown/poor fuse or poor fusebox connection feeding Terminal 15
Wiring harness damage or high resistance in feed to ECU(s)

Fault status

⚠️ Status

Terminal 15 (ignition-switched power) low voltage detected — ignition feed below expected level. May cause ECU/ignition failures, starting issues, and multiple secondary faults.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-2 hours

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P1600 — Power Supply Terminal No 15 Low Voltage