What Does P2538 Mean?
The PCM has detected an abnormally high voltage signal in the ignition switch ACCESSORY position circuit. This indicates voltage above the expected threshold, typically caused by a short to power in the wiring or a faulty switch.
Common Causes
35%
Short to voltage in ACC position wiring harness
30%
Ignition switch internal short causing high voltage output
20%
Damaged or pinched wiring creating short to power source
10%
Corroded connector causing voltage bleed from adjacent circuits
5%
PCM internal circuit fault on ACC position input
Diagnostic Steps
1
Step 1: Disconnect ignition switch and measure voltage on ACC circuit at PCM side (should be 0V with switch disconnected)
2
Step 2: Check for short to voltage by measuring resistance between ACC circuit and battery voltage with ignition off
3
Step 3: Inspect wiring harness for damage, particularly where it may contact hot circuits or power sources
4
Step 4: Test ignition switch output voltage in ACC position and compare to manufacturer specifications
5
Step 5: Check for aftermarket wiring modifications that may be causing voltage feedback into ACC circuit
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
The PCM has detected an abnormally high voltage signal in the ignition switch ACCESSORY position circuit. This indicates voltage above the expected threshold, typically caused by a short to power in the wiring or a faulty switch.
The most common cause of P2538 (Ignition Switch Accessory Position Circuit High) is: Short to voltage in ACC position wiring harness
Typical repair costs for P2538 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Low immediate safety risk. May cause accessories to operate when they shouldn't or prevent proper ignition switch position recognition by the PCM.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2538 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition System / Accessory Power System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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