Input-shaft-speed input circuit failure
Your transmission's computer can't read the input shaft speed sensor signal properly, like a speedometer that's suddenly gone blind. This prevents the transmission from knowing how fast the engine is spinning relative to the wheels, disrupting shift timing and control.
The ECU monitors the input shaft speed sensor signal frequency to determine turbine speed in the transmission. It expects a valid AC voltage signal that varies with shaft rotation speed. If the signal is absent, erratic, or out of the expected frequency range, the ECU flags a fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Input Shaft Speed Signal Frequency | Proportional to engine RPM (typically 0-10 kHz range) | No signal, constant signal, or frequency outside calibrated range |
| Signal Voltage Amplitude | 0.2V to 5V AC, varying with speed | Below 0.2V, above 5V, or constant DC value |
Code C1429 is classified as a serious fault. If your check engine light is flashing — not just steady — pull over safely and do not continue driving. A flashing CEL indicates an active misfire or critical failure that can cause catalytic converter damage within minutes or permanent engine harm within miles. Contact a certified mechanic immediately. Do not attempt roadside repairs on high-severity codes unless you are trained to do so.
Once the fault is repaired, C1429 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.