Symptoms
Symptoms of a P2509 engine code may include:
- Malfunction Indicator Light (MIL) illuminated with P2509 DTC
- Hard starting or failure to start
- Tachometer may fluctuate between 500-700 RPM at idle
- Check gauges light may illuminate and voltmeter shows 11 volts or less
- Truck may stall while driving
- Additional codes P2502 – charging system error and P2503 – low charging system output may accompany P2509 code
Potential Causes
Causes of this DTC may include:
- Battery failure
- Poor connection at batteries
- Alternator overcharging or undercharging
- High voltage drop across loose or corroded cables
- Electric clutch fan shorted to ground
- Poor connection at ECM
- Leaking diode
- Battery positive shorted to ground or other circuits
- Open ground or return circuit
Diagnostic and Repair Procedures
Special note for Dodge/Ram Cummins diesel owners: Technical Service Bulletin (TSB) number 18-001-07 may apply to your 2006 and newer truck which will fix it. The fix for this bulletin is to reprogram the PCM. You may also see the “Check Gauges” warning light and have DTC P2502 and/or P2503 with it.
Test batteries for charge. Use a voltmeter and place probes on both terminals. A fully charged battery will show approximately 12.75 volts. If batteries are below 12 volts, charge them before continuing. It’s useless to test a discharged battery.
In dual battery setups, if one battery is noticeably lower than the other battery, it’s probably bad. To clarify, the weak battery doesn’t take a charge at the same rate and likely has one or two bad cells. If caps are removable, remove them. Check the water level in all cells. If one or more are lower than adjacent cells, chances are the cells are bad.
With a hydrometer, check all cells. Good cells will have a density of 12.60. If all cells are equal but weak, a discharged battery is indicated. If one or more are below 12.60, the cells are shorted and the battery is bad.
If no hydrometer is available, use a voltmeter between terminals of freshly charged batteries. Try to start the engine and note the voltage drop on both batteries. If voltage drops below 10.5 volts, the battery is bad. At 32-degree temperatures, voltage should not be below 9.5 volts.
If the battery (batteries) doesn’t take a full charge, they’re bad. If they’re bad under any of the above circumstances, replace them. But this isn’t the end of the story. Why they’re discharged or bad is the next question to answer.
Check that all battery cables are not loose or corroded. If batteries took a charge, there’s a drain or bad cable. Check battery terminals and follow the cable to the end. Make sure they’re tight and the ground is secure and clean.
Look for broken insulation with exposed and corroded wires.
Start the engine and use the voltmeter to check voltage across battery terminals. If voltage is below 13.5 or above 15 volts, the regulator is faulty in the alternator. Stop the engine and replace the alternator. If voltage was equal to or above 13.5 and below 15 volts, proceed to next check.
Check for parasitic drain. This test requires a test light and voltmeter. Remove the negative terminal from one of the batteries. Make sure everything is turned off, including the glove box light. Doors should be closed and no circuits should be operating.
Wait 15 minutes for all systems to go to sleep. Set the voltmeter to amps and install one of the test light probes on the battery negative and the other wire on the red probe of the ammeter.
Install the black probe of the ammeter on a good ground. There should be less than 30 milliamps of draw. If it’s less, stop here. If the draw is higher, unplug the 6-pin connector from the electric clutch fan and see if the draw dropped – if so, replace the clutch fan. Otherwise, reconnect the connector and disconnect the negative cable from the opposite battery.
Remove the red battery cable from the back of the alternator. Recheck. If the drain drops, one of the diodes is leaking in the alternator. Replace the alternator. Otherwise, reconnect the alternator and the negative battery cable to the other battery.
Check ECU connections assuming everything else is good but batteries are draining. To check the ECU, look in the fuse block under the hood and remove the ECU fuse and recheck. If the draw drops, the ECU connectors or the computer itself is bad. If no draw was observed, replace the fuse. Remove the test light and volt/ammeter.
Systematically remove one fuse at a time and check the fuse terminals with the ammeter. Any circuit with excessive draw is the faulty circuit or component.
