A 2008 Toyota Camry Hybrid with more than 200K on the clock came in with the complaint of poor power and fuel economy. Since this was the Camry owner’s first time to our shop on another customer’s recommendation, I needed some detailed background information on the vehicle. After conducting an in-depth interview with the Camry owner, I uncovered some very important information. The hybrid owner revealed that the 2.4L motor had recently been rebuilt along with other repairs that were performed. When I questioned him on why the motor had to be rebuilt, he responded stating that the motor was consuming a quart of oil in 500 miles or less.
I continued my questioning to find out if there were any other repairs done to the vehicle, particularly on the high voltage system. Once again, more information was revealed that provided me with these insights — a new high voltage battery, new catalytic converter, air-fuel sensor, oxygen sensor, spark plugs, and fuel pump assembly had been installed.
I asked who performed the repairs and was told that a repair shop where he lives had performed all the repairs except for the HV battery replacement. The high voltage battery was replaced by a Toyota dealer in the Bronx near his job. With the information provided, I was now up to speed feeling that I had a good understanding of the vehicle’s history.
Time to look for myself
The next step was to perform a good look-see of the vehicle, concentrating on the engine and other related parts that he stated were replaced. This was followed by connecting the Toyota Techstream scan tool and performing a Health Check (Figure 1). As you can see from the scan tool screenshot there were four DTCs. The DTCs were U0293 (Lost Communication with Hybrid Control Module), B1421 Solar Sensor Circuit (Passenger Side), B1424 (Solar Sensor Circuit Abnormal) and B2281 ("P" Signal Malfunction).
This led me to go in for a deeper look by clicking on the specific DTCs (Figure 2 and 3) U0293 and B2281 to see if they were current or in history. The reason that I was not concerned with the other two DTCs (B1421 and B1424) was based on my past experience — they always set if the vehicle is not in direct sunlight. Starting with the most critical DTC U0293, I utilized all my SI systems (ALLDATA, Identifix, ProDemand, and MotoLogic) to dig up any additional information that could be useful. This was followed by a check on Google, YouTube and iATN that did not yield any useful "silver bullets."
What I discovered was that the DTC is set when communication with Hybrid Vehicle Control ECU is interrupted. This could have been caused by a voltage interruption or a voltage drop that needed to be checked. The DTC information listed a number of possible causes that included the wire harness, hybrid vehicle control system or the ECU. Wow, some help! It sounds like the usual list of components that make for an expensive repair.
I decided to hold off performing the wiggle, jerk, feel and massage test of the wiring harness or performing any voltage drop testing since further investigation needed to be performed. The reason that I did not perform those tests or replace any of the suggested components was that the DTC coded as a history code. I thought that I should move on to the next important DTC, the B2281, that also coded as a history code. The cause of the B2281 could be a "P" Signal Malfunction Cable information and CAN information between the main body ECU and shift lock control ECU inconsistency. Possible causes included the shift lock control, ECU or the wire harness or connector. Knowing that the motor was removed and rebuilt, I thought that the codes were most likely set by the repair and were not cleared. I decided not to waste my time and the customer's money by checking the list of the possibly defective components that may lead me nowhere.
Real or "ghost?"
The next most logical step was to erase all the DTCs, then road test the vehicle to see how it performed, followed by performing another scan tool Health Check. After I returned from the test drive, I informed the Camry owner that there were some problems that I needed more time to check out. The results of the post road test Health Check were (Figure 4) P3190 Poor Engine Performance, (Figure 5) P0A0F-204 (Engine Failed To Start) and a P0A9D-123 (Hybrid Battery Temperature Sensor "A" Circuit Low). I printed out the DTC reports and explained to the hybrid owner that I would need at least two additional hours to diagnosis these problems. The customer agreed, leaving me the vehicle to check out so I could call him with an estimate of the repairs.
The first DTC that I was going to dig into was the P3190 that can be caused by a communication with HV ECU, engine RPM at a fixed value or more, engine start mode not active, target torque at a fixed value, ratio of estimated torque against target torque could be less than 20 percent, air induction system issue, throttle body issue, fuel pressure problem, ICE (Internal Combustion Engine), mass airflow meter, out of fuel, engine coolant, temperature sensor, crankshaft sensor or camshaft sensor or the hybrid vehicle control ECU.
Now, that’s a mountain of problems to check out and would take additional time so once again I held off performing any testing. I moved on to see what would cause the P0A0F-204 (Engine Failed To Start) that was current along with an engine that would not start after the test drive. The cause of the no start DTC had a list such as abnormal signal input from the ECM (abnormal engine output), Hybrid control ECU or ECM problem. Carefully looking at the Freeze Frame for this DTC I noticed that the high voltage battery blocks were in range, so I ruled the HV battery out as a possible problem, even though the battery SOC (State of Charge) was at the low end limit of 41.6 percent. The last DTC P0A9D-123 (Hybrid Battery Temperature Sensor "A" Circuit Low) to check could be the cause of the complaint of no start, low power and poor mileage that the owner experienced.
After looking up the code definition and seeing the problem indicated circuit low voltage, I suspected that the circuit was shorted or had a severe voltage drop issue. When I find a code definition that states circuit voltage high, I look for an open or short to power. In this case, I am going to look for the opposite, something that is pulling down the circuit voltage making system voltage low. My next step was once again to check the DTC on my information systems. In many cases, I start with Identifix since they do an excellent job with tracking common DTC faults. Unfortunately for me, there were no exact or similar DTCs listed. Next, I performed a Google and YouTube search just to see if I can find any useful information. In many cases, if something is common either one or both of these websites are going to provide me with some helpful information. The same search was performed on iATN only to find out that there was nothing related to this Camry’s problem.
Moving the search back to MotoLogic and ProDemand provided some good information to read through and become more familiar with the code setting criteria. Both SI’s had useful information on specification’s but I needed to know more about how the system works, so I went into ALLDATA where I was able to find a good system description. When I am not familiar with a system, I like to read up on how the system operates and functions, so I have a complete understanding of what I am working on. Now, you're probably thinking it's a damn temperature sensor that is a basic negative coefficient, which means resistance and voltage are high when the temperature is cold and the opposite when hot. You would be correct, but I needed to know the location of the sensors, how many there are, where the voltage signal goes and what is the effect. Assuming the purpose of these sensors is to provide information on battery temperature, that in turn engages the high voltage cooling fan to operate for battery cool down.
After reading through the system description I found that the HV battery uses four temperature sensors that are located on the bottom of the HV battery at different locations that are similar to other Toyota hybrid HV batteries. These thermistors vary voltage as the HV battery temperature changes. Lower battery temperature = higher resistance or Higher battery temperature = lower resistance. The signal from the sensors goes to a Battery Smart Unit (HV Computer) that uses the battery temperature sensors information to detect the HV battery temperature levels. The sensors send the detected voltage values to the hybrid vehicle control ECU. Based on the temperature, the hybrid vehicle control ECU adjusts the HV battery blower fan for optimum battery cooling.
If the temperature reading of the HV battery temperature sensor is lower than a predetermined limit (short circuit) or is higher than a predetermined limit (open circuit) P0A9D123 DTC will set. Understanding how the system functions made it easy to check each resistor reading using scan data for the sensor value followed by double-checking the reading using my voltmeter. I used the sensor values from the resistance chart that was in service information (Figures 6 and 7) to compare to the reading on my scan tool and meter.
Now that I completed a check of scan data, voltmeter, and ohmmeter checks I was confident that the sensors were not the problem of this DTC. Service information had suggested checking scan data in the HV Battery ECU - PID Temp of HV battery TB 1 to 4 (resistors) in the HV ECU data list. If the sensors are in specification move on to the next step, if not replace the sensor. Since I tripled checked all the sensors using the test that I described I was sure that the sensors were not causing the problem.
Now here is where it gets painful and expensive, the SI stated if the reading is not in specification, replace the HV battery. It suggested testing the connection points at the described connections with an ohmmeter. If all the resistance is 10K or higher, replace the Battery Smart Unit. If the readings are less than 10K, replace the HV battery. One thing to remember is that the Camry had a new Toyota factory replacement HV battery installed recently and the battery pack scan data readings were normal, so it ruled out it being the cause of the DTC. The fix for this DTC was found by a good understanding of the system and its components along with proper testing of the circuit. The reading exceeded the OE specifications that indicated that the Battery Smart Unit was faulty.
I found a used control unit in a salvage yard and installed it then rechecked the system. When using a new or reconditioned HV battery you must transfer over the old control section of the battery case. The control section consists of the HV ECU/ Battery Smart Unit, SMRs (system main relays), current sensor and associated wiring. With the Battery Smart Unit replaced the HV system was back to normal and the P0A9D123 DTC was no longer be present.
"No start" next
The only thing left was to concentrate on was the "no start" issue that could have something connected to the rebuilt engine. A careful look at the rebuilt engine led me to believe that the rebuilt was far from a professional one. The engine looked like a backyard mechanic had made the repairs since I found some bolts missing, wire ties holding stuff together and many uncleaned engine components. After a bit more investigation I found that Toyota would have replaced this motor for free, parts and labor, due to the oil consumption problem. Speaking to the Toyota dealer, I was told that the Camry owner could submit his invoice for the engine rebuild and other related repairs to Toyota for reimbursement if it met their requirements.
Moving on to the "no start" and taking everything into account I went right on to basic engine testing. What do I normally do if an engine does not start, I asked myself? Well, I would check to see if it's getting air by installing a vacuum gauge on a good intake port then cranking the engine over, looking for 3 to 5 inches of cranking vacuum. The cranking vacuum test would indicate the timing components are working, no broken timing belt, chain or camshaft and that the engine is getting some air.
The next step would be to check for fuel, that is easy enough for me since I have a gas analyzer. All I had to do is place the exhaust probe into the tailpipe and crank the engine over if there is a reading of 2000 PPMs or more HCs coming out the tailpipe it’s good.
Since I had enough HCs the next step is to check for enough spark. On this engine, there have to be at least 45 KVs to start and burn the fuel, testing indicated that I had over 45KV, so that ruled out spark. Now the only thing left is compression but before I start to remove a spark plug, I know that I must check the engine for proper breathing. You can't get five pounds of crap out of a one-pound bag, so I removed the newly installed air-fuel ratio sensor and installed my vacuum/back pressure gauge.
This test would reveal the problem for the Camry's no start (Figure 8). So even though this vehicle had the rebuilt engine, new converter, air-fuel ratio sensor and other components including a new Toyota HV battery it came down to the basics. The fix for this Camry Hybrid had nothing to do with the suggestions on the trouble chart but rather a problem with the basics. Look at the real problem (Figure 9) — a clogged secondary converter.
Once the engine and exhaust cooled down, I was able to start the engine and measured 1 ¼ lbs of backpressure at idle. As the engine and the exhaust heated up the backpressure bounced up to 4 psi as the throttle was lifted off idle. The clogged converter was the cause for all the DTCs except for the P0A9D123 DTC HV ECU/ Battery Smart Unit. If the ICE has an issue it is going to cause an HV battery issue due to a problem performing as designed for charging and regeneration. Once again it comes down to the BASICS!
I hope this case study helps your diagnosis and repair hybrid vehicles. Always use proper personal protective equipment and get high voltage training before attempting to work on any vehicle that has an HV system. Work smart, be safe!
