P0738 code meaning
TCM Engine Speed Output Circuit Low
What P0738 means
Some transmission modules pass an engine speed signal on to other devices such as a tachometer over a wire of their own. CARB requires output circuits to be checked. No manufacturer document available to us uses P0737–P0739 – engine speed is shared over CAN today; the description follows CARB and the engine module's own speed output (P0654), which sends, for example, two pulses per revolution. P0738 means this output is too low, typically shorted to ground, so it can no longer switch high. The opposite is P0739, the general fault P0737. A tachometer or dependent display then reads zero or jumps, while driving is usually unaffected.
P0738 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0738
- Tachometer at zero or jumping
- Warning lamp depending on manufacturer
- Usually no effect on driving
Common causes of P0738
- Most likelyOutput wire shorted to ground
- PossibleReceiver shorted internally
- PossibleConnector corroded
- Less likelyDriver stage in the transmission module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Engine speed output circuitTachometerTransmission control module
What each part of P0738 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 7 | Area: transmission. |
| 38 | The exact fault in that area. |
What to do next
- Note P0738 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0738
What does P0738 mean?
P0738 means "TCM Engine Speed Output Circuit Low". Some transmission modules pass an engine speed signal on to other devices such as a tachometer over a wire of their own. It is a generic code, so it means the same on every make.
Is it safe to drive with P0738?
P0738 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P0738 fail an emissions test?
P0738 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0738 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0738 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.