Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P1678: Frame-To-Powertrain Torque Down Request Signal Line Malfunction (A/T Models Only)
2004 Acura 3.5RLSECTION DTC P1678: Frame-To-Powertrain Torque Down Request Signal Line Malfunction (A/T Models Only)
WARNING: This page is about a different car, the 2003 Acura 3.2TL and 2003 Acura 3.2CL. However, it is still accessible from the selected car via links, so may be relevant.
- Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. Start engine and wait 60 seconds. If DTC P1678 is set, go to next step. If DTC P1678 is not set, problem is intermittent. System is okay at this time. Check for poor connection(s) or loose wire(s) between PCM 20-pin "E" harness connector and ABS/TCS control unit 16-pin harness connector.
- Turn ignition switch off. Disconnect ABS/TCS control unit 16-pin harness connector. Start engine and wait 10 seconds. If DTC P1678 is set, substitute known-good ABS/TCS control unit, then recheck. If symptom or indication goes away, replace original ABS/TCS control unit. If DTC P1678 is not set, substitute known-good PCM, then recheck. If symptom or indication goes away, replace original PCM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.