AutoCodes – Generic – P18B7

P18B7 Code - Internal Mode Switch 'C' 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: P18B7 indicates Internal Mode Switch 'C' 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.

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Code Popularity 1,533

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Mar 23, 2024

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P18B7 Description

The internal mode switch indicates the Transmission Control Module (TCM) which gear position the vehicle operator has selected. The internal mode switch consists of 5 separate hall effect switches. Each hall effect switch is supplied with a 9 V reference circuit and a signal circuit from the TCM. Each signal circuit for each gear selector position will have either a voltage reading of 0.70–0.96 V indicating On or 1.68–2.38 V indicating Off. The voltage values on each internal mode switch circuit will change and are dependent on the position of the gear selector. The state of each internal mode switch A/B/C/P/S signal circuit is displayed on the scan tool. The Diagnostic Trouble Code (DTC) will be set when the TCM has detected the internal mode switch C signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B7 - Internal Mode Switch 'C' Circuit Shorted - AutoCodes.com — P18B7 Code - Internal Mode Switch 'C' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B7?

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 P18B7?

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 P18B7 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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Information for Specific Makes

P18B7 Buick — Internal Mode Switch 'C' Circuit Shorted
P18B7 Cadillac — Internal Mode Switch 'C' Circuit Shorted
P18B7 Chevrolet — Internal Mode Switch 'C' Circuit Shorted
P18B7 GMC — Internal Mode Switch 'C' Circuit Shorted

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P18B7 Code

1. What does OBDII code P18B7 mean?

P18B7 indicates that the Internal Mode Switch 'C' circuit in the transmission system is experiencing a short, causing improper communication with the transmission control module.

2. What are the common symptoms of code P18B7?

Symptoms may include difficulty shifting gears, the transmission stuck in one gear, erratic shifting, or the illumination of the check engine light.

3. What causes code P18B7 to appear?

The main causes include damaged wiring or connectors in the Internal Mode Switch 'C' circuit, a short to ground or power, or a faulty Internal Mode Switch.

4. Can I drive my car with a P18B7 code?

Driving with this code is not recommended, as it can lead to unsafe shifting or transmission damage. Itâ€™s best to address the issue promptly.

5. How is code P18B7 diagnosed?

A technician will inspect the wiring and connectors, test the Internal Mode Switch for functionality, and use a scan tool to monitor live data from the transmission system.

6. What tools are needed to fix code P18B7?

Common tools include a multimeter for testing circuits, a scan tool for diagnostics, and basic hand tools for repairing wiring or replacing the switch.

7. How much does it cost to repair a P18B7 code?

Repair costs vary but may range from $100 to $500, depending on whether the issue is with wiring or if the Internal Mode Switch needs replacement.

8. Can I fix code P18B7 myself?

If you have experience with electrical diagnostics and repairs, you can attempt to fix it by inspecting and repairing damaged wiring or replacing the switch. Otherwise, professional help is recommended.

9. What happens if I ignore code P18B7?

Ignoring this code can result in worsening transmission performance, potential damage to the transmission, and safety concerns while driving.

10. Is P18B7 a common code for all vehicles?

No, P18B7 is more specific to certain vehicle makes and models, typically those with electronically controlled transmissions using an Internal Mode Switch.