U0120 Mercury Code - Lost Communication With Starter/Generator Control Module
Quick Answer
The alternator is controlled by the Power Control Module (PCM) which monitors certain parameters such as the engine temperature, battery temperature and electrical demand. Common causes include Faulty Starter Motor, Faulty Generator/Alternator, Starter Motor harness is open or shorted. 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
- U0120 Mercury indicates Lost Communication With Starter/Generator Control Module.
- Common causes
- Common causes include Faulty Starter Motor, Faulty Generator/Alternator, Starter Motor harness is open or shorted.
- 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 U0120 Mercury Description
- The first thing to check is if the battery is the correct type. Smart charge systems are designed to be used only with a silver calcium battery not the lead acid type due to the voltages used which may damage a lead acid battery and give incorrect readings.
- If you disconnect the 3 pin PCM plug from the alternator and it is charging again, this will show the alternator is being controlled by the PCM. This will check if the alternator is still functioning. The 3 pin plug will need to be reconnected immediately after the test to avoid any damage to the vehicle. This test is a temporary check only and is not a resolution to the fault. Disconnection and reconnection of the 3 pin plug should be done when the engine is switched off.
If the battery is of the correct type and the alternator is found to be charging, the next part to check is the continuity of the wiring loom from the alternator to the PCM. Due to the location of the alternator in relation to the PCM, the wiring can become chafed or the insulation melts from being too close to a heat source. This is a common reason when the battery light is illuminated and a new loom will be needed.
What are the Possible Causes of the DTC U0120 Mercury?
- Faulty Starter Motor
- Faulty Generator/Alternator
- Starter Motor harness is open or shorted
- Starter Motor circuit poor electrical connection
- Generator/Alternator harness is open or shorted
- Generator/Alternator circuit poor electrical connection
How to Fix the DTC U0120 Mercury?
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 U0120 Mercury 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.
Need more information about the U0120 Mercury code?
Need more information on how to fix the U0120 Mercury code? Get Access to Factory Service Manuals
Need Help with the Code?
Get the U0120 Mercury code diagnosed by a professional: Find a repair shop in your area
Frequently Asked Questions about U0120 Mercury Code
1. What does the OBDII code U0120 mean on a Mercury?
U0120 indicates a loss of communication with the Starter/Generator Control Module (SGCM) on the vehicle's communication network.
2. What are the common symptoms of code U0120 in a Mercury?
Symptoms may include difficulty starting the vehicle, intermittent stalling, a no-crank condition, or the illumination of the check engine or warning lights.
3. What causes the U0120 code to appear on a Mercury?
Common causes include a faulty Starter/Generator Control Module, damaged wiring or connectors, network communication issues, or a low vehicle battery voltage.
4. Can a weak battery trigger the U0120 code on a Mercury?
Yes, a weak or failing battery can disrupt communication between modules and cause the U0120 code.
5. How do I diagnose the U0120 code on my Mercury?
Start by checking the battery voltage, inspecting the wiring and connectors to the SGCM, and using a scan tool to verify communication on the vehicle’s network.
6. Can I drive my Mercury with the U0120 code?
Driving with the U0120 code is not recommended, as it may lead to starting issues or other unexpected failures.
7. How is the U0120 code repaired on a Mercury?
Repairs may involve replacing or reprogramming the Starter/Generator Control Module, repairing damaged wiring, or resolving network communication faults.
8. Does the U0120 code mean the Starter/Generator Control Module is faulty?
Not necessarily. The issue could also stem from wiring problems, a weak battery, or other network communication issues.
9. How much does it cost to fix the U0120 code on a Mercury?
Repair costs vary but may range from $100 for basic wiring repairs to over $1,000 if the SGCM needs replacement or reprogramming.
10. Can a blown fuse cause the U0120 code on a Mercury?
Yes, a blown fuse related to the SGCM or communication network can cause the U0120 code to appear.
Discuss the causes and fixes for U0120 Mercury OBDII Code
Code U0120 Mercury comments
No comments found for this page.
Fix Your Car Smarter
Try the New AutoCodes App!
Get complete OBDII diagnostics, repair solutions, and cost estimates, plus AI chat support on demand.
