Scope & Scan - Service Repair

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Vehicles from the TST bays

War stories and lessons learned
Monday, November 2, 2015 - 08:00
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We decided to look at the current engine data that still displayed the LTFT at 44.48 percent, along with the AF sensor at 3.15 volts. The AF sensor reading from a normal running engine should be at 3.3 volts at idle and not what was currently being displayed. An important fact to remember is voltage under 3.3 volts is a reading that the engine is running rich, while a reading over 3.3 volts indicates the engine is running lean. Our problem Rav 4 AF sensor confirmed the P0171 DTC that it set in the Engine Control Module (ECM), now all we had to do is find out the root cause.

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Looking carefully at the current engine data revealed that HO2S B1S2 (the oxygen sensor after the converter) was reading 0.0 volts. As we raised and lowered the idle, we monitored the rear sensor expecting to see a change in the voltage, but it did not. Could a rear sensor cause our problem of high LTFT command? The answer is yes and here’s why: on many engines, the B1S2 sensor has authority to adjust fuel trim. On this vehicle it would have been easy to blame or replace a load sensor or other sensor without finding the cause of the problem. We ordered a new Toyota rear oxygen sensor, installed it and reset the fuel adaptation. Once the repair and the procedure were completed, we drove the vehicle until the monitor was “Ready.” As you can see by the after repair engine data (Figure 3), the LTFT was down to 9.34 percent while the AF sensor voltage reading was at 3.275 volts, just about the perfect 3.3 volts that Toyota recommends at idle.

Next on the list

A 2015 Acura MDX came in from a body shop that I do work for with a problem with a DTC B1E77 Blind Spot (open in the right side BSI radar unit indicator circuit) (Figure 4). The possible causes associated with this DTC are problems with the signal line open, ground harness open, indicator driver failure or right BSI indicator failure. The description tells it all, an open circuit means that something has been disconnected or broken open. The fix for this vehicle was simple thanks to the information provide with the DTC description. The problem was as simple as removing the passenger door (Figure 5) and connecting the open connector then clearing the DTC.  

Figure 3 Figure 4 Figure 5

This type of DTC is becoming more and more popular as many vehicles are being outfitted with lane departure and front and rear radar systems. Take a look at the 2014 Caddy ATS that I had to clear a DTC and reset and relearn the Long Range Radar Module. The process is very involved since it entails more than just reading and clearing the DTC. In fact, the module has to be programmed with the GM GDS and then be relearned while driving the vehicle at different speeds. The vehicle has to be driven for 10 to 30 minutes at different speeds while the radar system makes adjustments as the vehicle approaches other vehicles or objects on the road. Once the system has learned the low speed calibration, the scan tool prompts the operator to accelerate to a higher speed to perform the next calibration. This procedure adds more time to programming many of the vehicles that are on the road using a radar system. Some European and Asian vehicles need special lane departure /radar alignment (Figure 6) tools that have to be used to reset the systems.

Since this is my last regular TST “Scope and Scan” column, I want to thank all of you, especially those of you that have been kind enough to email me your comments. I hope that these articles have been helpful and have shed some light on the problems you find in your bays. Oh, I’ll still be writing feature articles for Motor Age and look forward to some new writers I’ve been hearing about that I am sure will provide all of us with some great information.

Figure 6


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