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P0738 Generic (SAE) Basic entry

TCM Engine Speed Output Circuit Low

Updated 2026-10-02 · Transmission

Severity
Medium
Typical repair cost
40 – 350 EUR
System
Powertrain

What it means

P0738 is stored when the engine control module measures a voltage in the TCM Engine Speed Output circuit that stays below the expected minimum. In practice this points to a short to ground, a damaged wire or a failed component rather than a mechanical problem.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

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Symptoms

  • Check engine or transmission warning light
  • Harsh, delayed or missing shifts
  • Transmission stuck in one gear (limp mode)
  • Shuddering or slipping under load

Common causes

  1. Damaged, chafed or corroded wiring in the TCM Engine Speed Output circuit
  2. Corroded, loose or water-damaged connector terminals
  3. Failed TCM Engine Speed Output component (sensor, solenoid or actuator)
  4. Poor ground connection for the module or component
  5. Faulty control module driver (rare, confirm all else first)

How to diagnose

  1. Read freeze frame data and note when the code set (cold start, under load, after rain)
  2. Inspect the TCM Engine Speed Output connector for bent pins, corrosion and water; wiggle the harness with the engine running and watch live data
  3. Measure supply voltage and ground at the connector with the key on
  4. Check the signal wire for shorts to ground or battery and for continuity to the control module
  5. Test or substitute the TCM Engine Speed Output only after wiring and connectors are confirmed good
  6. Clear the code and complete a drive cycle to confirm the repair

Frequently asked questions

Can I keep driving with P0738?

Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.

Will clearing P0738 fix it?

No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.

Related codes

P0739

Nearby codes in this group