TCM Engine Speed Output Circuit
The transmission control module isn't receiving proper engine speed signal data, like a missing phone line between two offices trying to communicate. This prevents the transmission from shifting correctly because it can't sync with engine RPM.
The ECM sends engine speed (RPM) data to the TCM via the CAN bus network. The TCM expects a continuous, valid signal within a specific frequency range. If the signal drops out, becomes erratic, or stops entirely, the fault is triggered.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Engine Speed Signal Frequency | Continuous valid CAN message every 10-20ms | Signal missing, delayed >100ms, or corrupted data |
| Signal Voltage/Data Validity | 0.5V-4.5V stable CAN bus state | Out-of-range voltage or bus timeout |
Code P0737 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0737 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.