Volkswagen P1602 Code: Power Supply (B+) Terminal 30 – Voltage Too Low
The engine computer saw its constant battery feed drop too low – usually a disconnected, flat or weak battery.
At a glance
Severity: Low
- Meaning
- Power Supply (B+) Terminal 30 – Voltage Too Low
- System
- ECU & Outputs · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $0–$750
- DIY difficulty
- Easy
In VW wiring, terminal 30 is the permanent battery-positive feed that keeps the engine computer's memory alive even with the key off. P1602, shown by VCDS as 18010 'Power Supply (B+) Terminal 30: Voltage too Low', is stored when that feed sagged below what the ECU needs. Most of the time it's a harmless memory of the battery being disconnected, run flat or jump-started, and it clears for good once the battery is healthy. If it keeps returning – especially with the EPC light, stalling or several modules logging voltage faults – look at the battery, its terminals and fuse holder, the ground straps and the alternator. It's mainly seen on Mk4-era and early Mk5 VWs; later cars use generic codes like P0562 instead.
Can I keep driving? Usually fine to drive. If the EPC light comes on or the engine stalls, have the battery and charging system tested before you get stranded.
Try this first – 5-minute fix
- Think back to recent battery work If the battery was disconnected, replaced, run flat or jump-started, P1602 is simply a stored record of that. Clear it and see whether it returns.
- Check and charge the battery A rested battery should read about 12.5–12.7 V. Below 12.4 V, charge it fully and have it load-tested; a battery that won't hold charge needs replacing.
- Clean and tighten the terminals Remove corrosion from the posts and clamps, check the fuse holder on top of the battery, and tighten everything so it can't be turned by hand.
- Clear the code and relearn Clear the fault, then on drive-by-wire engines run the throttle body adaptation with a scan tool so the idle settles correctly after power loss.
How to read P1602
- P Powertrain
- 1 Manufacturer-specific
- 6 Computer & outputs
- 02 Specific fault
Symptoms
- P1602 (VCDS 18010) found during a scan, often marked intermittent
- Code appeared after battery replacement, disconnection or a jump start
- EPC light, unstable idle or stalling right after reconnecting the battery
- Slow cranking on cold mornings
- Voltage-related codes stored in other modules at the same time
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Battery was disconnected, ran flat or the car was jump-started (stored event only)
- Aging or weak battery dropping too far during cranking
- Corroded or loose battery terminals or battery-top fuse holder
- Corroded ground strap between battery, body and engine
- Alternator or voltage regulator undercharging
- ECU power supply relay, wiring or connector fault
- Parasitic drain flattening the battery overnight
Diagnosis step by step
Measure battery voltage in three states
Check resting voltage (12.5–12.7 V), the lowest voltage while cranking (should stay above about 9.6 V) and charging voltage at 2,000 rpm (roughly 13.8–14.7 V). A deep dip while cranking means a weak battery or poor connection.
Tools: Multimeter
Voltage-drop test the cables
While cranking, measure between the battery negative post and the engine block, and between the positive post and the starter or fuse holder output. More than about 0.3–0.5 V across a connection means corrosion or a loose joint.
Tools: Multimeter
Scan all modules
Run a full auto-scan. If many modules logged low-voltage faults at the same time, the cause is common: battery, main cables or grounds. If only the engine ECU has it, check its own supply relay, fuse and connector.
Tools: OBD-II scanner
Check for parasitic drain
If the battery is repeatedly low in the morning, measure current draw once the car has gone to sleep; it should be well below 50 mA. A higher draw points to a module or accessory staying awake.
Tools: Multimeter
Relearn after repair
Clear codes, perform the throttle body adaptation where applicable and drive a full cycle. The code should not come back.
Tools: OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Charge battery and clean terminals | Yes | $0–$50 |
| Replace battery | Yes | $150–$300 |
| Replace corroded ground strap or battery fuse holder | Yes | $40–$200 |
| Replace alternator | No | $350–$750 |
| Repair ECU power relay or wiring | No | $80–$300 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Audi
Audi A4 B5/B6 and TT store the same 18010/P1602; when several modules show it together, the battery and main ground are the first place to look.
Emissions / smog test impact
Depends
P1602 usually doesn't light the check engine light, so it doesn't fail an OBD-II test on its own. But disconnecting the battery resets readiness monitors – drive for a few days before testing.
Frequently asked questions
Is P1602 serious?
Usually not. Most of the time it's a leftover record of battery work or a flat battery. It only becomes a real concern when it keeps returning with stalling, the EPC light or slow cranking.
What is terminal 30?
It's the German DIN designation for the permanent battery-positive supply, live even with the key off. Terminal 15 is the ignition-switched supply, and terminal 31 is ground.
How does P1602 differ from P0562?
P0562 is the generic 'system voltage low' code, usually tied to the charging system while running. P1602 is VW's own code for the ECU's permanent supply, and it's commonly stored after the battery was off or very low.
What does VCDS show?
Typically '18010 – Power Supply (B+) Terminal 30: Voltage too Low, P1602 – 35-10 – Intermittent'. Ross-Tech lists it as 18010/P1602/005634.
Sources
- Manufacturer public service information (cross-checked)
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