What Does P1600 Mean?
This code indicates the PCM is detecting low voltage on the ignition-switched power supply line (terminal 15/KL15). This terminal provides operating power to the PCM when the ignition is on. Low voltage can cause erratic PCM operation, incorrect sensor readings, and unstable engine performance. The issue is typically upstream in the vehicle's power distribution system rather than in the PCM itself.
Common Causes
25%
Weak or failing vehicle battery unable to maintain voltage under load
25%
Faulty alternator with low charging output
20%
Corroded or loose battery terminals or ground straps
15%
High-resistance connection in the ignition switch or power distribution circuit
15%
Blown or corroded fuse/fusible link in the PCM power feed
Diagnostic Steps
1
Measure battery voltage with the engine off (should be 12.4V+) and running (should be 13.5–14.7V); low readings indicate battery or charging system issues.
2
Perform a voltage drop test on the battery cables, ground straps, and PCM power feed circuit while the engine is running and loaded.
3
Inspect the ignition switch power feed circuit fuses and fusible links for corrosion or partial failure.
4
Check the PCM connector for signs of terminal corrosion, heat damage, or loose pin fit on the power supply pins.
5
If the battery and charging system check out, trace the KL15 power feed from the fuse box to the PCM, looking for high-resistance connections.
Estimated Repair Cost
$50 - $500
Parts + labor, varies by vehicle and location
This code indicates the PCM is detecting low voltage on the ignition-switched power supply line (terminal 15/KL15). This terminal provides operating power to the PCM when the ignition is on. Low voltage can cause erratic PCM operation, incorrect sensor readings, and unstable engine performance. The ...
The most common cause of P1600 (Power Supply (B+) Terminal 15 Low Voltage) is: Weak or failing vehicle battery unable to maintain voltage under load
Typical repair costs for P1600 range from $50 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Low voltage to the PCM can cause erratic engine behavior, stalling, and incorrect sensor readings. In severe cases, it may cause loss of engine power while driving. The vehicle's safety systems that rely on PCM data may also be compromised.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1600 to identify the root cause.
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Quick Info
Category
Powertrain
System
PCM Power Supply / Electrical System
Difficulty
Type
Manufacturer
Recommended Tools
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