Practical checks and shop questions for EPC/ETC and throttle-related codes; save evidence before replacing parts.
This is a non-invasive owner checklist, not an OEM repair procedure or permission to drive.
This reference supports the stated topic only. Model, model year, equipment, current rule or individual vehicle conditions may differ; check the original source before acting.
Read the Ford original: 1999 Powertrain Control/Emissions Diagnosis DTC descriptions Source date: document date not recorded; research checked: 2026-11-01.
Codes in this diagnostic topic
These codes share a system-level checklist, but their distinct numbers and meanings are shown below. A code here does not prove a particular vehicle has every listed fault. Use the exact code row and full scan.
| Code | Meaning | Vehicle scope |
|---|---|---|
| P0121 | Throttle-position signal performance mismatch | Exact vehicle scope unverified |
| P0122 | Throttle-position signal low | Exact vehicle scope unverified |
| P0123 | Throttle-position signal high | Exact vehicle scope unverified |
| P0506 | Idle speed below expected target | Exact vehicle scope unverified |
| P0507 | Idle speed above expected target | Exact vehicle scope unverified |
Save the evidence first
- Warning steady/flashing
- Idle quality and available power
- Throttle/pedal codes and full vehicle identity
Safe owner checks
- Move to safety if power delivery is unpredictable.
- Record the message without operating a phone while driving.
Questions for a qualified technician
- Are sensor plausibility, wiring, actuator movement or another engine-control fault responsible?
- Are adaptation/calibration steps required after a confirmed repair?
Common wrong turns
- EPC or a lightning bolt does not prove a bad throttle body.
- Do not manipulate an electronic throttle plate or run actuator tests using generic instructions.
Confirm the repair
- Have the shop verify reliable control and required adaptations.
Sources and scope
- Ford — 1999 Powertrain Control/Emissions Diagnosis DTC descriptions Document: date not recorded · Research checked: 2026-11-01
- Volkswagen USA — Warning and indicator lights Document: date not recorded · Research checked: 2026-11-01
- Jeep / Stellantis — 2025 Wrangler Owner’s Manual, US/Canada Document: date not recorded · Research checked: 2026-11-01
- Ford — Gasoline OBD System Operation Summary MY 2024–2025 Document: 2024-04-16 · Research checked: 2026-11-01
- Ford — OBD System Operation Summary, gasoline 2020–2023 update Document: 2023-10-23 · Research checked: 2026-11-01
Research snapshot: 2026-11-01. Source documents may have newer revisions. Verify current instructions and VIN eligibility with the manufacturer.