Assalamu Alaikum, readers of The Auto Pulse! Today we have a classic case study on a Toyota Corolla 1.3 (NZ-Series). The customer recently replaced the car battery, and immediately after, the car developed a serious problem.
The Symptoms: The Check Engine Light is ON, the RPM is fluctuating (unstable idle), and the car has lost acceleration. Even with the pedal floored, the RPM won't go above 1800. This is known as "Limp Mode."
In this guide, we diagnose the P2118 Trouble Code and reveal a hidden fuse box issue that often happens after battery work. Watch the full diagnosis below.
1. Scanning for DTCs (P2118)
We connected the scanner and found two codes. One was for the O2 sensor (P0137), but the critical code causing the power loss was:
This code means the computer (ECM) isn't detecting the correct current flow to the Electronic Throttle Body. When this happens, the car cuts power to prevent damage.
2. Understanding the ETCS Circuit
Looking at the wiring diagram, we can see that the Electronic Throttle Control System (ETCS) gets its power directly from the battery through a specific fuse.
- +BM: Power Source from Battery.
- ETCS Fuse (10A): Protects the throttle circuit.
- ECM: Controls the throttle motor.
Since the problem started after a battery change, checking the power supply (Fuses and Terminals) is the first logical step.
3. The Hidden Fault: ETCS Fuse
We located the ETCS 10A Fuse in the engine bay fuse box (2nd row, bottom). At first glance, the fuse looked unbroken. However, upon closer inspection, we found the real issue.
The loose connection caused resistance and heat, which actually caused the fuse plastic to "glow" or melt slightly, even though the wire inside wasn't blown. This loose contact prevented proper voltage from reaching the throttle motor.
4. The Fix & Final Results
We repaired the fuse box by pulling the pin back up to ensure a tight connection and installed a fresh 10A fuse.
The Results:
- The Check Engine Light turned off automatically.
- The RPM stabilized.
- Full acceleration was restored.
Lesson Learned: If you lose acceleration after a battery change, don't rush to replace the Throttle Body or Computer. Always check the ETCS Fuse and its connection first!
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