When I was a young man in the early eighties, I was told the following wise words by a gentleman whose age I now reflect (Old): “Why is there never time to do something right but always time to do it over again.” Now, I can reflect on that statement more than I want to admit.
A Toyota 4Runner with an A340F transmission came to our shop. The customer stated that the vehicle would “Delay forward in the morning and had shifting problems in the morning at start.” Due to being occupied myself, the original road test was done by another technician who informed me that he did not feel any problems.
It was a very hectic week for me (one of those when everything seemed to go wrong). The following morning, when the same technician did the road test, he informed me that it took off in high gear for the first few moments and then started to shift correctly.
The vehicle had no codes and no PID data to observe. We had recently purchased a solenoid Kit for a similar vehicle with a TCC problem and only used the TCC solenoid, so we had the two shift solenoids left over. I informed the technician to replace the shift solenoids because they are prone to fail and figured that one was failing mechanically. The following morning, the same problem persisted.
This same technician informed me that he had located an inexpensive ECM locally. Being very occupied, I figured, what the heck, throw it on. You guessed it, same problem. Time to do the proper diagnosing.
Since the problem was likely to show up in the morning, I back-probed the ECM Pin #7 (S1) and pin #8 (S2) of the E9 connector and left the vehicle ready for road test first thing in the morning.
The following morning, as I watched the graphing meter, when I turned the ignition ON, the problem was staring me right in the face: Bad battery. As Figure 1 shows, with the ignition on, there were only 9.43 volts present at Shift Solenoid 1. After starting the vehicle, the ECM had SS1 and SS2 with no voltage, placing the transmission in 4th gear (Figure 2). After driving for about 25 seconds, the ECM came alive and placed the transmission in 2nd gear in accordance with the speed I was driving (Figure 3). A few stop-and-go’s and then a long road test revealed the transmission to operate properly. Replacing the battery was the solution to the problem.
Looking back (they say hindsight is 20/20), I can see how I assumed wrong. The vehicle had no problem cranking even with low voltage. The battery would charge up but would not hold voltage overnight. You had to leave it parked for a while for the problem to arise. With no codes and no data to see, it meant more time to go directly to the horse’s mouth, as they say: back probing the ECM.
Normally, it is standard procedure to get as much information from the customer, obtain and document codes, road test with a scanner, and record a drive cycle movie (If available) to review at the shop.
If an electrical problem is suspected, then a proper electrical check should be done. Which includes the Battery-open voltage test, voltage drop test on the negative and positive side of the battery cables, battery voltage test during cranking, and checking the health of the charging system. Capacitors do not like battery voltage to drop below 8.5 volts during engine crank as this reset learned values stored in the ECM memory. With a good charging system but with a weak battery, that was our problem. When the battery voltage became low, the cranking voltage would drop below 8.5.
What is the lesson? Many times, because of being too busy or because we assume. We fail to do the basics. This may cause us to lose more time than we were trying to save. Well, there is always time to do it again!
