Don’t fear Asian vehicles! Since many companies already share parts and technology, you will notice that Asian vehicle are not that much different than domestic vehicles. Just like any other vehicle that comes into your shop with a problem, you need a game plan on how you’re going to address the problem.
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2010 Toyota 4Runner
Our first vehicle is a 2010 Toyota 4Runner 1GR-FE with 128k that came in with the ABS light illuminated and the owner complaint of a braking issue. We started our diagnosis with a Q&A of the owner, followed by a short test drive and a visual inspection before connecting our scan tool.
After we connected the Toyota TechStream scan tool (Figure 1) we found the following DTCs; C1404 (Open or Short in Rear Speed Sensor LH Circuit), C1408 (Open or Short in Rear Speed Sensor LH Circuit) and C1416 (Open in the Sensor Signal Circuit of a Malfunction area occur 255 times or more). Our next step was to take a look at the DTC supporting information - Freeze Frame. As you can see from the Freeze Frame data (Figure 2), the Left Rear wheel speed was recorded moving at 0 mph, while the other wheels were displaying 26 to 27 mph.
The source of the DTC could be caused by the rear speed sensor, skid control sensor wire, speed sensor circuit, speed sensor rotor and/or the master cylinder solenoid skid control ECU. Common problems with theses sensors include debris, a sensor that has moved from its normal position and defective sensors. We took the vehicle for a test drive with the scan tool connected, making sure we drove it in a straight line at 28 mph to see if the DTC would reappear. The DTC returned right away so there was no need to drive the vehicle in reverse at two mph as recommended by Toyota.
With the test drive confirming that the circuit had a problem, my lead technician (Bill) checked the wiring to make sure there were no connection problems. After the wiring checked out, the next step was to call the 4Runner owner and recommend that both rear wheel speed sensors be replaced. Take notice, that we did not use a labscope on this problem since Toyota service information had specific testing of the circuit that would confirm the problem without using any other tool besides the Toyota Techstream. Why take out the backhoe when a shovel will do the job? We need to remember that we sell our time to the customer, so we need to diagnosis the problem in the easiest and most efficient way.
2005 Toyota Tacoma
A 2005 Toyota Tacoma with a 1GR-FE V6 4.0L came in with an overheating issue and the MIL on. This vehicle had 123,938 miles on the clock and has served our customer very well over the years. After we connected our scan tool, we discovered that the MIL was illuminated due to a misfire in number 6 cylinder.
As Bill began his diagnostic game plan, he came upon a low coolant level as part of his preliminary checks. He also found that the scan data displayed a P0306 DTC that could be caused by a mechanical, ignition, or fuel issue. He proceeded to check all the easy stuff first, performing a relative compression test, ignition and fuel system test. After performing a basic cooling system pressure test that failed to hold pressure, his next step was to check for a head gasket problem since this is a common issue on this Toyota V6 engine. Bill’s decision to proceed in this direction was based on the test results from the relative compression test that indicated normal results, while the cooling system pressure test failed.
His next logical step was to check for CO2 in the cooling system using the ATS Bullseye CO2 tester. In our shop, we have had excellent results while using the BullsEye tester to uncover head gasket or cylinder head issues. On this vehicle, the test results indicated CO2 levels that could be the result of a cylinder head gasket, head or engine block problem. You may be thinking that we should have used the engine block tester that uses the liquid blue dye and changes color when there is a compression leak issue. Our experience with the block test has not always been good or accurate enough at detecting problems.
While using the ATS Bullseye CO2 leak detector, we uncovered (Figure 3) a CO2 leak that was displayed by the tool’s led bar illuminating along with an audible alert. The confirmation provided by the Bullseye tester was what we needed to inform the vehicle owner that we would need extra diagnostic time. Our next step in the confirmation process was to perform a cylinder leak down test in order to complete the diagnosis of this engine. Notice, we did not perform a compression test since we already confirmed that the engine’s relative compression was within range, the cooling system had already failed the pressure test, and now the leak detector was indicating high CO2 levels in the coolant.