Asian case studies from the shop

Our first Asian vehicle issue has the number one DTC in the country, P0420 (Figure 1) Catalyst Efficiency Below Threshold, Bank 1. This problem vehicle had 199,815 miles on the odometer, and that was presented to us with only a pending DTC (since the shop had previously erased the code).  

The shop this vehicle came from thought the rear O2 sensor was faulty and replaced both with new ones, only to end up with the same results. When the shop owner called me, he asked if we could diagnose the problem Land Cruiser. With the vehicle in our possession, we proceeded to perform a visual inspection, followed by connecting the eSCAN (our number-one scan tool for driveability and illuminated MIL issues). The results of the eSCAN yielded the following:  

• Pending P0420 
• Three Monitors “Not Ready” (Figure 2) 
• Mode 6 Bank 1 Catalyst failure (Figure 3) 
• Graphed data of the O2 sensors that revealed the front and rear sensor voltages were dithering (Figure 4) on both banks. 

With the result at hand, our next step was to look up TSBs and connect the Toyota TechStream (Toyota factory scan tool) to perform a full vehicle scan. After the TechStream was finished checking all the vehicle systems, it revealed there was a program update available for the PCM. We followed the Toyota online update that provided information on the new reflash (Figure 5) to address a P0136 “Oxygen Sensor Circuit Malfunction Bank 1, Sensor 2,” and P0156 “Oxygen Sensor Circuit Malfunction Bank 2, Sensor 2.”  

Just what the doctor ordered! Remember that the other shop had replaced the rear O2 sensors then erased the DTCs. With the OPUS/DrewTech CarDaq M J2534 tool already connected, we proceeded to perform the reprogramming process. After a brief period, the programming process was completed, and the flash calibration update screen displayed successful results. The next step was to perform a Run-Rite carbon cleaning in an attempt to get the catalytic converter back to life and keep the MIL from illuminating. The process was successful, as displayed on the eSCAN Mode 6 data (Figure 6) confirming that the vehicle was fixed and ready to ship. 

2007 Honda Accord 2.4L  

In the past, a common failure component on Hondas was the main relay. The only problem with this Honda is that it does not have the typical main relay; rather, it uses a starter cut relay. We located the starter cut relay under the left lower dash in the fuse box, where we noticed that there were at least a couple of the same four-pin numbered relays. You know where this is going (Yup, the “swap the relay” game). Swapping the relays can be a wise and time-efficient move to perform to rule out a defective relay.  

Franklin (my tech who was working on the vehicle) performed the switch and retested the vehicle to see if it would start before moving on. Since the switch of the relay did not remedy the problem, Franklin proceeded to test the available voltage, ground, and relay pins for continuity on this normally open relay. Following AllData service information, Franklin found that all the relay terminals tested good, so he moved on to the next logical component, the ignition switch.  

Franklin proceeded to remove the cover from the steering wheel upper column, allowing him to connect his meter leads to the terminals, then wiggle, feel, jerk, and massage the wiring to see if there were any voltage dropouts. Since the test was not conclusive, Franklin decided to connect the eSCOPE to the pins and see if there were any dropouts while he turned the ignition key to the “start” and “off” positions.  

Making the right move allowed Franklin to uncover the intermittent no-start condition that was due to a faulty ignition switch (Figure 7). It had worn out and needed to be replaced. He called the Honda dealer, who informed him the part was not in stock, but they could get it in a week or so. In our shop, our go-to move is to check NAPA and WORLDPAC first went it comes to ordering parts. Since NAPA did not have the part in stock and WORLDPAC did, Franklin was able to order just the electrical switch component, without the entire ignition key assembly. When the new part arrived, Franklin installed it, retested, and confirmed the problem was the ignition switch, since the engine started every time the ignition key was turned. With the vehicle now operating trouble-free, we called the Honda owner and told him he could come pick it up. 

2011 Honda Pilot 3.5 L V6 

 This next vehicle came in with a complaint of poor shifting and transmission light flashing as the vehicle was driven. To start our diagnosis, we connected the Honda i-HDS scan tool and recovered a P0733 (64-3), “Problem in 3rd Clutch and 3rd Clutch Hydraulic Circuit.”  

We looked up the code information in AllData and followed the prescribed diagnostic procedure. With the engine already warmed up to proper operating temperature, we checked the transmission level, which was up to the fill mark. With 87,000 miles on the clock, the fluid was dark and dirty, so it needed to be changed as a good first step. We decided to drain the fluid and look for excessive metal debris and clutch material but did not find any.  

Our next step was to follow the service information and check the main-line pressure, which was found to be in specification. This was followed by checking the third clutch pressure, which was not up to the Honda specification. The next step was to test all the shift solenoids, all of which passed the spec. Now what?  

We thought, “What else could be causing the shift problem and the blinking light?” and considered it was the messenger (aka the pressure switch). Bingo! After comparing the scan data pressure information to the pressure gauge, we located the problem. We called the Honda dealer and ordered the transmission switch, part number 28610-R36-004.  

After installing the switch, we rechecked the fluid level then test drove the vehicle. The test drive did not reveal any transmission shifting problems, DTCs, or illuminating lights. Mission accomplished; the Pilot was back to shifting and running like new.  

2008 Toyota Tundra 5.7L V8 

This Toyota with 121K miles on the odometer was towed in for a no-start condition, along with no vehicle communication with the scan tool. The dashboard had the four-wheel low light, VSA (vehicle stability assist), and traction control lights all flashing. Having seen this problem before, we knew where it was likely going to lead us.  

With no vehicle communication, we decided to connect a BOB (breakout box) to make sure that we had battery voltage at pin 16 and chassis ground at pin 4. With both pins operating at the specified levels, we decided to move on to the communication connections by checking pin 6 (CAN high) and pin 14 (CAN low) using the eSCOPE.  

The results on the scope displayed waveforms that were pulled down below their normal levels. The next logical step was to look up the wiring diagram in ProDemand and check all the voltage and ground supply circuits. Results of the tests were all normal. We needed to find what was causing the CAN lines to be pulled down. Again, with our previous experience on a few other Tundra's, we decided to check the AIR (air injection reaction) system pump solenoids that are located on both banks of the engine. When we removed the wire connector from Bank 2 (attached to the air pump) we lucked out. The CAN communication came right back. For added assurance, we checked the service information and found information in Identifix that matched our problem (Figure 8). It always makes sense to check Identifix and other information systems, making sure we test and not guess, preventing an expensive mistake.  

The service information stated that the resistance of the solenoid should be between 0.4 to 1 ohms. With an ohmmeter connected between the two air pump connector terminals, it measured 0.2 ohms. As we know, lower resistance causes high amperage that can take a computer out (or in this case, pull down the CAN bus). With the solenoid wire disconnected, the engine started right up. This confirmed the problem component, so we ordered a new air pump, installed it in the vehicle, and shipped the vehicle. 

2013 Subaru Legacy 

This Subaru Legacy (like a few others we’ve had in the shop recently) has a shifting problem. One of our customers had a complaint that his 104,000-mile Legacy had the transmission temperature light flashing. Checking service information, we found a TSB -- number 16-91-14 --that described the issue on the transmissions and relates to diagnostics for the lockup solenoid and shift solenoid circuits.  

Following a logical procedure, we checked the vehicle for codes by running a complete vehicle scan. The results of the scan came up with a DTC P2762 “Lock-up Duty Solenoid Malfunction” that we had seen before on Subaru vehicles. With the information at hand, we moved on to check the transmission fluid that was at the fill line but exhibited a dark color and a burned smell.  

My tech Bill was working on this vehicle and took the next step setting up the eSCOPE (Figure 9). The scope leads were connected as followed: 

• Channel 1 (YELLOW)= Lock-up solenoid control circuit voltage. The control circuit’s job is to send a pulse to modulate single to the solenoids that change the duty cycle.  
• Channel 2 (RED)=  Lock-up solenoid current. This is what provides an amp reading showing the work performed with the lock-up solenoid was operating.   

As you can see by the red waveform, there was close to no current draw on the lock-up solenoid. Unfortunately, Subaru does not offer a separate lock-up solenoid for sale, so we had to order the complete valve body. Bill drained the fluid and performed a transmission service, then installed the new valve body. After the repair, the scope was once again connected to the vehicle that revealed completely different waveforms (Figure 10) on both voltage and current. With the repair completed, the next step was to clear the DTC and take the vehicle for a spin. The road revealed that the vehicle was shifting properly, no codes present — along with no lights on the dash illuminated -- and another one bites the dust.  

2001 Nissan Pathfinder 3.5L V6  

 Our last vehicle has 142,000 on the odometer, and it came in with an illuminated MIL. This was caused by a P0171 “System Too Lean Bank 1” (Figure 11). The LTFT (long term fuel trim) on both banks in Freeze Frame was at +16%  at 57% load/ 2025 RPMs, and 57 mph.  

Our next step was to check the Fuel Trim chart (Figure 12) on the eSCAN, where we found elevated numbers from the bottom of the chart to the top (all operating ranges). We know when we come across this problem that we need to check the MAF sensor. We moved from the fuel trim chart to the VE chart (Figure 13) and inserted the correct altitude and temperature before we performed the test. With all the correct information inserted, we proceeded to perform the test, where the results indicated a MAF failure.  

With both the fuel trim and VE test failing, we know that even though there was no MAF sensor DTC that there was a MAF problem. We removed the air filter and checked to see if there was any debris in the hose or near the MAF, and everything looked good. That confirmed to us that the MAF was defective, so we recommend a new MAF to the vehicle owner and proceeded to install it. 

With the new MAF installed, we erased the DTC and took the vehicle for a road test. The results were no DTCs, no pending DTCs, or illuminated check engine lights. Look at the fuel trim chart after the replacement, which proved the PCM is no longer commanding excessive fuel (Figure 14).  

Take notice that the Fuel Trim numbers are mostly negative trims. Do you know what we needed to do to correct the negative numbers? I am betting you know that clearing codes does not reset the additive fuel trims. Without clearing the trims, the engine will take time to get back in proper control. After a lean condition, rich condition, or MAF DTC, we always reset the additive fuel trim, either by the scan tool (if it has the option), or by turning the ignition key or power button "off” and removing both cables from the negative and positive post of the battery. We then connect a 1 ohm/10-watt resistor between the cables for at least 10 minutes. The resistor will bring down all the capacitors in all the vehicle’s computers slowly. With the adaptive trim reset, the vehicle was back in fuel control and running great. We returned the vehicle to the owner, got paid for what we diagnosed and repaired correctly.  

I hope that this article with Asian cases studies from our shop is helpful for you to diagnose and repair vehicles.