P2D57 code meaning
Generator B Control Circuit Range/Performance
What P2D57 means
P2D57 belongs to a second alternator, called generator B, as fitted to some heavy trucks; GM, for instance, offered a secondary generator (option KHB) on 2019 Silverado medium-duty trucks with the 6.6 L diesel. The code concerns the control channel of that machine: the engine computer's command and the regulator's response do not fit together, or the signal leaves its plausible band. No manufacturer documents P2D57 publicly. Infineon's LIN regulator chip TLE8881-3 shows what such a regulator reports: an electrical error flag for a field terminal shorted to ground or battery, an open field winding or excessive battery voltage, debounced over 250 or 1,000 ms; if communication stops, it falls back to a default set point. Generator A uses P065B. The charge lamp may light.
P2D57 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2D57
- Charge warning lamp or message
- Second alternator charges at a fixed default voltage or not at all
Common causes of P2D57
- Most likelyDamaged control line (LIN or command wire) or corroded connector
- PossibleFaulty voltage regulator of the second alternator
- Less likelyReplacement alternator with an incompatible regulator
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Generator bVoltage regulatorWiring harnessECM
What each part of P2D57 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 57 | The exact fault in that area. |
What to do next
- Note P2D57 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2D57
What does P2D57 mean?
P2D57 means "Generator B Control Circuit Range/Performance". P2D57 belongs to a second alternator, called generator B, as fitted to some heavy trucks; GM, for instance, offered a secondary generator (option KHB) on 2019 Silverado medium-duty trucks with the 6.6 L diesel. It is a generic code, so it means the same on every make.
Is it safe to drive with P2D57?
P2D57 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P2D57 fail an emissions test?
P2D57 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P2D57 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will P2D57 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.