P1681moderate severityPowertrain
A/T FI Signal A Low Input
on 2020 Honda Accord 1.5L I4 Turbo · FWD
What this code means
The automatic transmission control unit detects a low voltage on the A/T FI signal A line to the PCM. This is a Honda manufacturer-specific code with no direct generic OBD-II equivalent.
Symptoms
- Transmission warning light
- Harsh or erratic shifting
- Reduced engine performance
Common causes
- Short to ground in signal wire
- Faulty TCM output
- Poor connector contact
- PCM input fault
Diagnostic steps
- Retrieve transmission and PCM codes
- Inspect A/T FI signal A wiring
- Measure signal voltage at PCM
- Test TCM and PCM circuits
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P0004
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P0010
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P0011
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P0013
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P0014
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P0015
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