What Does B1478 Mean?
This code indicates that the Body Control Module (BCM) has detected simultaneous activation of both the one-touch up and one-touch down signals for a power window circuit. This represents a logical impossibility since a window cannot be commanded to move in both directions at the same time. The BCM has recognized this as a fault condition, typically caused by a short circuit, faulty switch, or internal BCM logic error affecting the power window control system.
Common Causes
45%
Faulty or internally shorted power window master switch assembly
30%
Short circuit between power window switch wiring harness conductors
15%
Water or liquid contamination in window switch causing internal bridging
10%
Body Control Module internal fault or software glitch
Diagnostic Steps
1
Step 1: Perform visual inspection of the affected window switch for signs of liquid contamination, physical damage, or burnt contacts. Remove switch assembly and inspect connector terminals for corrosion or pin damage.
2
Step 2: Using a digital multimeter, disconnect the power window switch connector and test for continuity between the one-touch up and one-touch down signal wires with switch disconnected. There should be infinite resistance (open circuit) between these conductors.
3
Step 3: With switch disconnected, use multimeter to check for short circuits to ground or voltage on both one-touch signal wires. Both should show open circuit with ignition off, and proper reference voltage (typically 5V or 12V depending on manufacturer) with ignition on.
4
Step 4: If wiring tests pass, reconnect switch and monitor BCM data stream using scan tool while slowly actuating window switch through all positions. Observe one-touch up and one-touch down input states - only one should activate at a time.
5
Step 5: If simultaneous signals are observed with known-good wiring, replace the power window master switch assembly. If no simultaneous signals are observed but code returns, suspect BCM internal fault and verify by substituting BCM if possible or checking for technical service bulletins.
6
Step 6: Clear codes, cycle window switch through all functions multiple times, and road test vehicle to confirm repair. Monitor for code recurrence.
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected simultaneous activation of both the one-touch up and one-touch down signals for a power window circuit. This represents a logical impossibility since a window cannot be commanded to move in both directions at the same time. The BCM ...
The most common cause of B1478 (Power Window One Touch Up/Down Activated Simultaneously) is: Faulty or internally shorted power window master switch assembly
Typical repair costs for B1478 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This fault does not affect vehicle safety or driveability. The affected window may not operate or may operate in manual mode only. Repair can be scheduled at convenience, though it impacts convenience and comfort features.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1478 to identify the root cause.
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Quick Info
Category
Body
System
Power Window Control System
Difficulty
Type
Manufacturer
Recommended Tools
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