A failing generator bearing or internal mechanical drag causing excessive heat; A shorted or faulty voltage regulator inside Generator B leading to overcharging and overheating; Restricted cooling airflow to the generator, such as a blocked duct or debris-packed fins; A damaged or corroded generator wiring harness causing high resistance and heat; An overloaded electrical system from aftermarket accessories drawing too much current; A faulty temperature sensor inside Generator B giving a false over-temperature reading

DTC codes / P2Dxx · Hybrid propulsion / P2D59

P2D59Generator B Over Temperature

Q: What does code P2D59 mean?

Generator B Over Temperature. P2D59 indicates that the engine control module has detected an over-temperature condition for Generator B, which is the second generator or alternator in a multi-generator system. The computer sets this code when the generator's internal temperature sensor reports a value above the calibrated threshold, typically due to excessive electrical load or a cooling fault.

P2D59 indicates that the engine control module has detected an over-temperature condition for Generator B, which is the second generator or alternator in a multi-generator system. The computer sets this code when the generator's internal temperature sensor reports a value above the calibrated threshold, typically due to excessive electrical load or a cooling fault.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaHybrid propulsion

Symptoms you may notice

Illumination of the battery or charging system warning light on the dashboard
Reduced charging output or a completely dead battery if the generator shuts down to protect itself
Electrical accessories such as lights or infotainment dimming or malfunctioning
A burning smell or visible smoke from the generator area in severe cases
Often no symptoms besides the warning light, especially if the generator is still producing some charge

Common causes, most likely first

A failing generator bearing or internal mechanical drag causing excessive heat
A shorted or faulty voltage regulator inside Generator B leading to overcharging and overheating
Restricted cooling airflow to the generator, such as a blocked duct or debris-packed fins
A damaged or corroded generator wiring harness causing high resistance and heat
An overloaded electrical system from aftermarket accessories drawing too much current
A faulty temperature sensor inside Generator B giving a false over-temperature reading

How to diagnose and fix it

Perform a visual inspection of Generator B for debris, damaged cooling fins, or a seized bearing
Use a scan tool to check live data for Generator B temperature and charging voltage to confirm the over-temperature condition
Test the generator's output with a carbon pile load tester to verify it meets specifications under load
Inspect and clean all generator electrical connections, including the battery terminals and ground straps
Check for aftermarket electrical accessories that may be overloading the charging system and disconnect them temporarily
If the temperature sensor is accessible, test its resistance against specifications and replace if faulty
Replace Generator B if internal faults such as a bad bearing or regulator are confirmed

Generator B overheating: beyond the obvious

A common oversight is a slipping or glazed serpentine belt that drives Generator B, which reduces its speed and causes it to work harder and overheat without obvious noise.
The code can be set by a faulty temperature sensor inside the generator even when the unit is not actually overheating, so always verify with live data before replacing the generator.
High-resistance in the generator's output cable or ground circuit can cause the generator to overcharge and overheat, and this is often missed when only the generator itself is tested.
On vehicles with two generators, the second unit often runs only under high electrical demand, so the over-temperature code may only appear during specific driving conditions such as towing or heavy accessory use.
A weak or failing battery can cause the generator to run at maximum output continuously, leading to overheating and setting this code, so always load-test the battery as part of diagnosis.

Can I keep driving with P2D59?

You can drive a short distance to a repair shop if the charging system warning light is on and the battery is not draining, but avoid using unnecessary electrical accessories and do not embark on long trips. If the battery voltage drops or the engine begins to stall, pull over safely and arrange a tow to prevent being stranded.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.