P0727 means the transmission control module received no engine speed input. Its family is P0725 (circuit), P0726 (range or performance), P0727 (no signal) and P0728 (intermittent). Engine speed is the reference the transmission uses to schedule shifts, control the torque converter clutch and detect slip. Without it, the transmission holds a safe gear.
Severity: moderate. Can you keep driving? To a shop. If the engine runs and the signal is missing only at the transmission, expect harsh or absent shifts, no converter lockup and a limp mode. If the crankshaft sensor itself has failed, the engine will not run at all, and the code is a companion to a no-start rather than the main event.
Two ways the signal reaches the transmission
Directly. Older designs and some current ones wire the crankshaft position sensor, or a dedicated engine speed sensor, to the transmission module. A fault in that sensor or its wiring sets P0727 whether or not the engine module has its own reading.
Over the network. Most current vehicles measure engine speed in the engine module and send it to the transmission module as a data message. If the message stops, the transmission stores P0727 while the engine runs perfectly, and the real fault is in the network or in the engine module's output, not in any sensor.
Which design the vehicle has decides everything about the diagnosis, and the scan tool tells you: if the engine module shows correct rpm while the transmission module shows zero, the signal is lost between them.
Causes, in the order they are found
A crankshaft position sensor or its wiring on direct-wired designs: a failed sensor, a chafed or open wire, a connector with oil or coolant in it, or a damaged reluctor ring. Usually with an engine that stalls or will not start.
A network fault on networked designs: a chafed bus wire, a connector, or a module reset from low voltage, usually with U codes stored as well.
A shared ground or reference with resistance, when several sensors drop out together.
The engine module's output to the transmission on designs with a dedicated wire between them.
The transmission module, last.
A diagnostic order
- Compare engine rpm in the engine module and in the transmission module on the scan tool with the engine running. Both correct means the fault is intermittent; engine correct and transmission zero means the link; both zero with the engine running means the sensor or its circuit.
- Record companion codes. P0335 through P0339 (crankshaft sensor) point at the sensor; U codes point at the network.
- On a direct-wired design, inspect the sensor connector, measure the sensor's resistance and its AC output while cranking, and check the wire to the transmission module for opens and shorts.
- On a networked design, check the bus wiring and the module power and grounds, and test the battery, since low voltage produces exactly this pattern.
- Repair what measured wrong, clear the code, and verify through a full shift cycle. Let the readiness monitors complete before an inspection.
Frequently asked questions
Can I drive with a P0727 code?
To a shop. The transmission holds a fixed gear without an engine speed reference, which is safe for a short distance but overheats the fluid on a long one. If the engine stalls or will not start, the crankshaft sensor is the priority.
Is P0727 the crankshaft position sensor?
On vehicles that wire the sensor to the transmission module, often. On vehicles that send engine speed over the network, the sensor is usually fine and the fault is between the engine and transmission modules. Comparing the rpm reading in both modules on the scan tool decides which.
Why does the engine run fine with P0727 set?
Because the engine module has its own valid reading and the transmission module does not. The signal was lost on the way between them, on a dedicated wire or on the network, or the transmission module is not receiving it for reasons of its own power and ground.
How much does it cost to fix P0727?
A crankshaft position sensor is an inexpensive part with a short replacement on most engines. A wire or connector repair is under an hour. A module is the expensive outcome and comes last.
Related codes
- P0725 / P0726 / P0728: engine speed input circuit, range, intermittent.
- P0335 to P0339: crankshaft position sensor circuit, the engine module's version of the same sensor.
- P0715 to P0718: input shaft speed sensor, the transmission's other speed reference.
- U0100 / U0101: lost communication between the engine and transmission modules; see U codes and module communication.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.