OBD-II Code
P0840
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$450–$2,200
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
P0840 logs when the TCM sees transmission fluid pressure sensor A return a signal voltage outside the expected window for the current line pressure command, or fails the rationality test against engine load and gear state.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Read the full diagnostic procedureP0840 logs when the TCM sees transmission fluid pressure sensor A return a signal voltage outside the expected window for the current line pressure c…
P0840 logs when the TCM sees transmission fluid pressure sensor A return a signal voltage outside the expected window for the current line pressure command, or fails the rationality test against engine load and gear state.
Start with the cheapest, highest-yield check
pull the dipstick or fluid-level plug and verify fluid level and condition at operating temperature, because aerated, overfilled, or burnt fluid causes pressure signal noise that mimics a sensor fault. Scan-tool the sensor PID at idle in Park; on most domestic platforms the sensor should read between 0.5V and 1.0V at 30-60 psi line pressure, ramping linearly to 4.0-4.5V at 220-280 psi during a 3-2 forced downshift. Caveat: pressure sensor A is almost always mounted inside the valve body or mechatronic assembly on modern boxes (6L80, ZF 8HP, 6T70, 62TE), so replacement requires pan-drop or full mechatronic R&R.
Vehicle-specific patterns2007-2013 GM 6L80/6L90 in Silverado, Tahoe, Camaro, and CTS-V has a known internal pressure sensor failure on the valve body that requires pan-drop a…
- 2007-2013GM 6L80/6L90 in Silverado, Tahoe, Camaro, and CTS-V has a known internal pressure sensor failure on the valve body that requires pan-drop and TEHCM replacement or sensor-only swap on later units.
- 2012-2016Chrysler 200 and Dodge Dart with the 62TE shows P0840 from a cracked solenoid block connector seal letting ATF into the wiring.
- 2009-2015Audi and VW with the ZF 6HP and 8HP transmissions throw P0840 most often after a mechatronic sleeve seal failure where fluid migrates into the TCM connector.
- 2014-2018Ford F-150 with the 6R80 sees P0840 from a failed main control valve body pressure switch.
Estimated repair$450 to $2200.
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