What Does P078A Mean?
The TCM has detected a malfunction in the Shift Timing Solenoid B circuit. This solenoid works in conjunction with Timing Solenoid A to provide precise control over shift event timing. When Solenoid B malfunctions, the TCM loses the ability to fine-tune shift overlap and engagement timing, resulting in shift quality degradation, particularly during specific gear transitions that rely on Solenoid B.
Common Causes
35%
Failed shift timing solenoid B (electrical or mechanical failure)
25%
Damaged or corroded wiring in the solenoid B circuit
20%
Corroded or damaged transmission connector affecting solenoid B pins
12%
Contaminated transmission fluid affecting solenoid mechanical operation
8%
TCM driver circuit failure for timing solenoid B
Diagnostic Steps
1
Measure shift timing solenoid B resistance at the transmission connector and compare to manufacturer specification.
2
Inspect the transmission connector for corrosion, moisture damage, or pin damage specifically on the solenoid B pins.
3
Check for proper voltage supply and ground at the solenoid when the TCM commands it to operate.
4
Monitor live data for timing solenoid B commanded state versus actual response to verify the TCM command signal.
5
If electrical tests are normal, check transmission fluid condition and inspect the valve body for restrictions.
6
Check for related TSBs or updated TCM calibrations that address timing solenoid B issues.
Estimated Repair Cost
$200 - $1,200
Parts + labor, varies by vehicle and location
The TCM has detected a malfunction in the Shift Timing Solenoid B circuit. This solenoid works in conjunction with Timing Solenoid A to provide precise control over shift event timing. When Solenoid B malfunctions, the TCM loses the ability to fine-tune shift overlap and engagement timing, resulting...
The most common cause of P078A (Shift Timing Solenoid B Malfunction) is: Failed shift timing solenoid B (electrical or mechanical failure)
Typical repair costs for P078A 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 but with degraded shift quality. Certain gear transitions may feel harsh, delayed, or poorly timed. The condition does not typically pose an immediate safety risk but should be repaired to prevent progressive transmission wear.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P078A to identify the root cause.
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Quick Info
Category
Powertrain
System
Automatic Transmission
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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