OBD-II Trouble Code Technical Description

ECM/PCM Power Input Signal Intermittent

What does that mean?

This is a generic powertrain code, which means it covers all makes supporting OBD-II protocol. However, specific troubleshooting steps will vary depending on the vehicle.

The generic trouble code P2509 power input signal intermittent refers to an engine with an intermittent electrical signal to the Electronic Control Module (ECM) otherwise also known as a PCM or Powertrain Control Module.

The signal is not constant and within parameters with the ignition key turned off. For one reason or another the voltage from the batteries is either low, is dropping due to a power drain or there is a bad connection.

A small amount of parasitic draw in the range of 30 milliamps or less is normal after all the computer have gone to sleep or timed out. The ECM memory and the radio memory are responsible for this, but it is insignificant and will not effect battery performance.

This code seems most common on Dodge & Ram diesel trucks. Technical service bulletins for the Dodge/Ram Cummins diesel engine also conclude that an overcharge or undercharge condition will also contribute to the setting of this code and the corresponding symptoms.

Symptoms

Symptoms of a P2509 engine code may include.

Malfunction Indicator Lamp (MIL) illumination with P2509 DTC set

Hard to start or failure to start

Tachometer may fluctuate between 500 to 700 rpm when idling cold

Check gauges light may illuminate and voltmeter displays 11 volts or less

Truck may cut off while driving

Additional codes P2502 – charging system error and P2503 – charging system output low may accompany the code P2509

Potential Causes

The causes for this DTC may include:

Battery failure

Poor connection at the batteries

Alternator is either overcharging or undercharging

Large voltage drop through loose or corroded cables

Electrical clutch fan short to ground

Bad connection at ECM

Leaking diode

Battery + positive shorted to ground or other circuits

Open or return ground circuit

Diagnostic and Repair Procedures

Special note for Dodge/Ram Cummins diesel owners: There is a technical service bulletin (TSB), number 18-001-07 that may apply to your 2006-older truck that will fix it. The fix for that bulletin is to reprogram the PCM. You may also see the "check gauges" warning lamp and have a P2502 and/or P2503 DTC along with this one.

Test the batteries for charge. Use a voltmeter and place the probes on both terminals. A fully charged battery will display about 12.75 volts. If the batteries are lower than 12 volts charge the batteries before proceeding. It is pointless to check a discharged battery.

Checking battery voltage using a digital voltmeter:

In the case of dual batteries, if one battery is notably lower than the other battery, it is probably bad. To clarify, the low battery is not taking a charge at the same rate and probably has a bad cell or two. If the caps are removable take them off. Look at the water level in all cells. If one or more are lower than the adjacent cells the odds are the cells are bad.

With a hydrometer check all the cells. Good cells will have 12.60 specific gravity. If all cells are equal but low, a discharged battery is indicated. If one or more are lower than 12.60 the cells have shorted and the battery is bad.

If a hydrometer is not available, use a voltmeter across the terminals of the freshly charged batteries. Attempt to start the engine and make note of the voltage drop on both batteries. If the voltage drops below 10.5 volts, the battery is bad. In 32-degree temperatures the voltage should be no less than 9.5 volts.

If the battery (batteries) won’t take a complete charge they are bad. If they are bad under any of the above circumstances replace them. But that’s not the end of the story. Why are they discharged or bad is the next question to answer.

Check all cables on the batteries for looseness and corrosion. If the batteries took a charge there is either a drain or a bad cable. Check the battery terminals and follow the cable to its end. Make sure they are 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 the voltage at the battery terminals. If the voltage is less than 13.5 or more than 15 volts the regulator is bad in the alternator. Shut the engine down and replace the alternator. If the voltage was 13.5 or better and less than 15 volts proceed to the next check.

Check for parasitic drain. This test requires a test light and voltmeter. Remove the negative terminal on one of the batteries. Make sure to turn everything off including the glove box light. The doors must be closed and no circuits working.

Wait 15 minutes for all the systems to go to sleep. Place the voltmeter on amps and install one of the test light probes on the battery negative and the other wire on the red ammeter probe.

Install the black ammeter probe on a good ground. There should be less than 30-miliamps draw. If it is less stop here. If the draw is higher disconnect the electrical clutch fan 6-pin connector and see if the draw dropped, if it does replace the clutch fan. If not reconnect the connector and disconnect the opposing battery negative cable.

Remove the red battery cable from the rear of the alternator. Recheck. If the drain drops, one of the diodes is leaking in the alternator. Replace the alternator. If not reconnect the alternator and the negative battery cable to the other battery.

Check the ECU connections assuming everything else is good yet the batteries are draining. To check the ECU look in the underhood fuse block and remove the fuse to the ECU and recheck. If the draw drops the ECU connectors or 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 defective circuit or component.