P1500 Code: Is Your Alternator Dying or Is It Just a Speed Sensor?

You scan your car, and P1500 pops up. If you Google it, you might get conflicting answers. That’s because P1500 is the chameleon of trouble codes—it means something completely different depending on the badge on your grille.

Why P1500 Confuses Even Experienced DIYers

Unlike universal codes (like P0300 for misfires), P1500 is manufacturer-specific. A cheap $20 code reader might just tell you "Manufacturer Control," leaving you in the dark. But a professional tool reads the specific definition for your ECU.

🔵 The Tale of Two Codes:

If you drive a Mitsubishi (Lancer, Outlander):
P1500 usually means "Generator FR Terminal Circuit." Basically, your alternator isn't communicating with the ECU correctly. Your battery might die soon.
If you drive a GM (Chevy, GMC) or Subaru:
It often points to the "Vehicle Speed Sensor (VSS)" or "Idle Control." Your truck might shift weirdly, or your speedometer might be acting erratic.

Stop Guessing, Start Seeing Data

Because the symptoms vary so much, throwing parts at a P1500 is a waste of money. You need to see what the computer is seeing. This is where the iCarsoft CR Ultra P shines.

It doesn't just read the code; it lets you view Live Data Streams to verify the failure before you buy a replacement part.

"We actually demonstrated how navigating these deep data streams works in our recent video breakdown. If you want to see the interface in action, check out our 2025 iCarsoft CR Ultra P Review & Video."

How to Troubleshoot P1500 (Step-by-Step)

Here is a logical workflow to diagnose this code using the CR Ultra P, depending on your vehicle make.

Scenario A: Mitsubishi (Alternator/Charging)

Voltage Check: Plug in the CR Ultra P. Go to Live Data in the Engine Module. Look for "System Voltage" or "Battery Voltage."
Load Test: Turn on your headlights and AC. Watch the voltage graph on the scanner.
- If it drops below 13.0V significantly, your alternator (or the FR signal wire) is likely the culprit.
- If voltage stays steady but the code persists, check the connector on the alternator for corrosion (a very common Mitsubishi issue).

Scenario B: GM / Subaru (Speed Sensor)

Drive Test: Select "Vehicle Speed" in the CR Ultra P data stream.
Compare: Have a passenger watch the scanner while you drive. Does the scanner's speed match your dashboard speedometer?
- If the scanner reads 0 mph while you are moving, your Output Speed Sensor (OSS) or VSS is dead or disconnected.

Frequently Asked Questions

Is P1500 serious?

On a Mitsubishi, yes—it means your charging system is compromised, and you could be left stranded with a dead battery. On GM/Subaru vehicles, it affects drivability and shifting, which can cause long-term transmission wear if ignored.

Can a bad battery cause P1500?

Yes. If your battery is old and cannot hold a surface charge, the ECU may interpret the voltage fluctuation as an alternator circuit failure. Always test your battery health first.

Where is the Vehicle Speed Sensor located?

For most P1500 cases on trucks and SUVs, the sensor is located on the tail housing of the transmission. It's usually an easy DIY swap, but you should confirm it's faulty with a scanner first.

"Seeing code P1501 instead? Check out our guide on Vehicle Speed Sensor & Idle issues here."