P18B5 2018 GMC Sierra Code - Internal Mode Switch 'A' Circuit Shorted
Quick Answer
The internal mode switch indicates the Transmission Control Module (TCM) which gear position the vehicle operator has selected. Common causes include Faulty Transmission Internal Mode Switch, Transmission Internal Mode Switch harness is open or shorted, Transmission Internal Mode Switch circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P18B5 2018 GMC Sierra indicates Internal Mode Switch 'A' Circuit Shorted.
- Common causes
- Common causes include Faulty Transmission Internal Mode Switch, Transmission Internal Mode Switch harness is open or shorted, Transmission Internal Mode Switch circuit poor electrical connection.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code P18B5 2018 GMC Sierra Description
What are the Possible Causes of the DTC P18B5 2018 GMC Sierra?
- Faulty Transmission Internal Mode Switch
- Transmission Internal Mode Switch harness is open or shorted
- Transmission Internal Mode Switch circuit poor electrical connection
- Faulty Transmission Control Module (TCM)
How to Fix the DTC P18B5 2018 GMC Sierra?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P18B5 2018 GMC Sierra code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
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Frequently Asked Questions about P18B5 2018 GMC Sierra Code
1. What does the OBDII code P18B5 mean on a 2018 GMC Sierra?
The P18B5 code indicates an issue with the Internal Mode Switch (IMS) 'A' Circuit, specifically a short in the circuit.
2. What are the common symptoms of P18B5 in a 2018 GMC Sierra?
Symptoms may include the transmission stuck in one gear, harsh shifting, erratic gear changes, or the check engine light turning on.
3. What causes the P18B5 code to appear?
Common causes include a shorted IMS wiring harness, a faulty IMS, corroded or loose connections, or a malfunction in the transmission control module (TCM).
4. How do I diagnose the P18B5 code in my 2018 GMC Sierra?
Diagnosis typically involves inspecting the IMS wiring for damage, checking for loose or corroded connectors, testing the IMS itself, and scanning the TCM for additional codes.
5. Can I drive my 2018 GMC Sierra with the P18B5 code?
While the truck may still be drivable, continued use could cause further damage to the transmission. It’s best to address the issue as soon as possible.
6. How do I fix the P18B5 code on a GMC Sierra?
Repairs may involve replacing damaged wiring, cleaning or securing connections, replacing the faulty IMS, or reprogramming/repairing the TCM.
7. What is the Internal Mode Switch (IMS) in a 2018 GMC Sierra?
The IMS is a component in the transmission that helps the vehicle’s computer determine the selected gear and mode of operation.
8. How much does it cost to repair a P18B5 code?
The cost depends on the root cause, but replacing the IMS typically costs $200–$500, including parts and labor. Wiring or TCM issues may vary.
9. Can a bad battery cause the P18B5 code?
While unlikely, low voltage from a failing battery can sometimes cause electrical issues that might trigger this or related codes.
10. Do I need to reset the code after fixing the P18B5 issue?
Yes, after completing repairs, clear the code with an OBDII scanner and test drive the vehicle to ensure the issue is resolved.
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