What Does P078B Mean?
The TCM has detected that Shift Timing Solenoid B is operating outside its expected performance range. The solenoid is responding to commands but not delivering the precise timing control needed for smooth shifts. This indicates gradual mechanical degradation of the solenoid, contaminated fluid affecting its precision, or valve body wear that reduces the solenoid's hydraulic effectiveness.
Common Causes
30%
Worn shift timing solenoid B with degraded mechanical response accuracy
25%
Contaminated or degraded transmission fluid affecting solenoid precision
20%
Valve body wear in the timing solenoid B hydraulic circuit
15%
Internal transmission wear affecting shift event feedback to TCM
10%
TCM adaptive shift values at their correction limits
Diagnostic Steps
1
Check transmission fluid level and condition — fluid degradation is the most common cause of gradual timing solenoid performance loss.
2
Monitor live data for timing solenoid B duty cycle and actual shift event timing to quantify the performance deviation.
3
Perform a transmission fluid and filter service, reset adaptive values, and perform a relearn drive cycle to see if the code clears.
4
If the issue persists, inspect the valve body for wear in the timing solenoid B bore that could reduce hydraulic precision.
5
Bench-test the timing solenoid B for response accuracy and compare to new-part specifications.
6
Verify no other related codes are present that might point to a broader transmission control issue.
Estimated Repair Cost
$200 - $1,200
Parts + labor, varies by vehicle and location
The TCM has detected that Shift Timing Solenoid B is operating outside its expected performance range. The solenoid is responding to commands but not delivering the precise timing control needed for smooth shifts. This indicates gradual mechanical degradation of the solenoid, contaminated fluid affe...
The most common cause of P078B (Shift Timing Solenoid B Range/Performance) is: Worn shift timing solenoid B with degraded mechanical response accuracy
Typical repair costs for P078B range from $200 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle is drivable with slightly degraded shift quality. Shifts may feel a bit rough or poorly timed but the vehicle remains safe to operate. Address the issue during routine maintenance to prevent progressive wear.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P078B to identify the root cause.
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Quick Info
Category
Powertrain
System
Automatic Transmission
Difficulty
Type
Generic (SAE)
Recommended Tools
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