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P0794 — Intermediate Shaft Speed Sensor Circuit Intermittent

Generic OBD-II · all makesPowertrain (engine & transmission)

P0794 indicates the powertrain or transmission control module has detected an intermittent signal from the automatic transmission's intermediate shaft speed sensor. The sensor reports the rotational speed of an internal transmission shaft, and an erratic or dropping signal can disrupt shift timing and torque-converter control. The code specifically points to a signal reliability or electrical circuit problem rather than a complete, steady failure.

Symptoms

What causes it — most likely first

1. Faulty intermediate shaft speed sensor

The sensor's internal winding, Hall element, or connector can degrade, producing an erratic or dropping signal while still occasionally working.

2. Wiring or connector fault

Intermittent open circuits, corrosion, pin fretting, chafed insulation, or poor grounds in the sensor harness are common causes of a circuit-intermittent code.

3. Damaged or contaminated tone ring

A cracked, chipped, or debris-covered reluctor ring can generate missing or inconsistent pulses that the control module interprets as sensor circuit intermittency.

4. Transmission fluid condition or level issue

Severely degraded, contaminated, or low fluid can affect sensor readings and transmission operation, though it is less often the direct cause of an intermittent circuit code.

5. PCM or TCM internal fault

A rare possibility is an intermittent processing fault in the control module; this should only be considered after the sensor, wiring, and tone ring have been ruled out.

How it's diagnosed

  1. Inspect the sensor connector and wiring for corrosion, bent pins, chafing, or loose terminals; wiggle-test the harness while monitoring live data.
  2. Check transmission fluid level and condition; correct level or replace fluid if it is low, burnt, or contaminated.
  3. Compare the sensor's resistance, voltage output, or waveform to manufacturer specifications; use an oscilloscope to look for signal dropouts.
  4. Remove and inspect the tone ring or reluctor wheel for cracks, missing teeth, metal debris, or physical damage.
  5. If the sensor and tone ring are good, verify power, ground, and signal continuity to the PCM/TCM; consider module testing only after all mechanical and electrical causes are excluded.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make

Frequently asked

Can I keep driving with P0794?

Short trips may be possible, but erratic shifting can worsen and lead to transmission stress; diagnosis is recommended promptly.

Is P0794 the same as an input or output speed sensor code?

No, it specifically monitors an intermediate shaft; the exact sensor location varies by transmission design.

Do I need a new PCM or TCM?

Usually not. PCM/TCM failure is uncommon for this code; most cases are caused by the sensor, wiring, or tone ring. Replace the module only as a last resort.

Will clearing the code fix the problem?

No. Clearing the code may turn off the light temporarily, but it will return if the intermittent signal fault is still present.