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Basically we need to find out why it's in limp home mode and address it. Knowing why the CEL is on would greatly improve odds of fixing things, or at least tell where to start. Since the car sat for a long time, you could have bad ported injectors. Maybe they have varnish on them. Basically you need to check air, spark and fuel. But before diving too deep into it, knowing why there is a CEL would be the way to start.
Here's chatGPTs recommendations, to take with a grain of salt:
If your Subaru BRZ has the Check Engine Light (CEL) on but your code scanner can’t read any codes, the issue is almost always in the communication path between the car’s ECU and your scan tool — or in the way the light is being triggered.
Here are the main possibilities:
1. OBD-II Port Power/Communication Issue
Blown fuse — The OBD-II port on the BRZ is powered by the same fuse as the cigarette lighter/12V outlet (Fuse #5 “Backup” or similar). If it’s blown, your scanner won’t communicate.
Corroded/loose OBD-II pins — Bent pins or corrosion can block data.
Aftermarket electronics — Remote starters, stereo installs, or security systems sometimes disrupt CAN bus communication.
Check:
Use a multimeter on pin 16 of the OBD port — should have 12V with ignition ON.
Check fuses in the interior fuse box.
2. Incompatible or Low-End Scanner
Some cheap OBD-II readers can only pull generic powertrain codes, not manufacturer-specific Subaru/BRZ codes.
If the CEL is for something stored in another module (ABS, TCM, body control), a basic scanner won’t see it.
Fix:
Use a scanner with CAN protocol + manufacturer coverage (e.g., Autel, Foxwell, Launch, or Subaru’s SSMIII software).
3. The Light Isn’t Actually the CEL
On the BRZ, the yellow “malfunction indicator” light can be confused with other warning icons (VSC, traction control, etc.).
If it’s a “Service Required” light, it won’t store OBD-II codes — just a mileage-based reminder.
4. ECU/Powertrain Communication Fault
A bad ECU ground, damaged CAN wiring, or a failing ECU can cause no comms + CEL.
Rare, but if the car recently had jump-starts or battery swaps, voltage spikes can damage ECU circuits.
5. Dead or Weak Battery
Low voltage during startup can light the CEL but cause incomplete code storage.
On the BRZ, anything below ~11.5V during ignition can make modules misbehave.
Quick Troubleshooting Path:
Check OBD-II fuse and power at port.
Verify scanner works on another car.
Try a higher-end scan tool with Subaru protocol.
If still nothing — inspect CAN wiring and ECU grounds.
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