Shift Pointers
- Author: Pete Luban
I’m sure most of you not only are familiar with the title of this article but also at one time or another have experienced it firsthand.
The vehicle came in for a transmission problem that you corrected after the necessary repairs, but now the vehicle has a problem that it did not come in with and, in some instances, is not even remotely related to the transmission work you performed.
So now you have a decision to make: Do I deliver the vehicle and claim “no fault,” which you know isn’t going to fly because there’s no way the owner of this vehicle is going to accept his or her vehicle in that condition, or do you try to correct the problem that occurred while the vehicle was in your possession?
First of all, what happened? What course of events took place to create this condition?
In many instances, during the repair process it is necessary for us to disconnect the battery or the computer. Sometimes this is all it takes to create a problem in the vehicle that was not there before.
Let’s take a look at some of these “disconnect”-related problems and how to correct them should this happen to you.
Problem #1
A 1996-98 Dodge truck or van or a Jeep is in the shop for repairs. The technician shuts off the ignition and quickly disconnects the black PCM connector shown in Figure 1. In the famous words of Arnold Schwarzenegger, “big mistake!”
On these vehicles, it has been found that under certain Key On or momentary Key Off conditions, when this connector is unplugged, the PCM may try to electronically write information to the EEPROM within the PCM.
Sometimes this inadvertent write will set the charging-system voltage to zero, preventing the charging system from charging the battery. If this occurs, the only fix is to replace the PCM.
We all know not to unplug computers with the ignition on, but the PCM connector shown in Figure 1 should never be unplugged unless the ignition has been off for a minimum of five seconds.
Problem #2
The next problem is a 1996 Dodge Caravan that has just had the transmission re-installed after an overhaul. The initial road test goes well, and the van is put back on the lift for a leak check. No leaks are found and the second road test goes well, but no one notices the flashing light on the rear-wiper switch. After all, we don’t do wiper repairs, do we?
Of course, five minutes hadn’t passed when the manager saw this van come back up the driveway. The customer complained about the flashing light as well as improper operation of the air-conditioning system.
First, this has nothing to do with wiper repair, but I think you’ve guessed that. Here’s the deal: The first thing the R&R technician did on this job was to disconnect the battery, and, of course, it remained disconnected until the transmission was ready for fluid.
When the battery is disconnected on these late-model vans, the HVAC (heating, ventilation and air-conditioning) system must be recalibrated. When this is necessary, guess which light starts flashing. You guessed it, the light on the rear-wiper switch. This is telling you that the HVAC system has lost its air-door calibration.
To recalibrate using the HVAC control panel, refer to Figures 2, 3 and 4.
If other lamps are flashing after you complete this procedure, the system has found faults and has stored related codes. I would say this is the time to give it to the A/C repair person.
Problem #3
Our next problem concerns a 1995 Cadillac Seville that has had the transmission repaired and has the same battery-disconnect situation. The technician clears all previous codes before the car is taken for its initial road test. During the road test the “Check Engine” lamp comes on. #@$&, I don’t have time for this *&#$! When the car returns to the shop, the technician connects the scan tool and retrieves code P080, “TP Sensor/Idle Learn Not Complete.”
What this is telling you is that when the battery is disconnected for a prolonged period, the PCM needs to have the throttle-position-sensor and idle-speed relearn procedure performed. Refer to Figure 5 for the procedure.
Before performing this relearn procedure, make certain that nothing is interfering with the accelerator or brake pedal, the heated window is turned off and there is no load on the power steering. If you do not take these precautions, the PCM will be unable to complete the relearn procedure.
If the code remains even after you perform this procedure, there may be faulty components, such as the throttle-position sensor, vehicle-speed sensor, transmission-range sensor, power-steering pressure switch or brake switch that prevent the procedure from being completed.
Problem #4
Our last problem child for this issue is a GM truck equipped with a 6.5-liter turbo diesel engine and a 4L80-E transmission with the same battery-disconnect scenario. When you take this vehicle for the initial road test, the Service Engine or malfunction-indicator lamp comes on, and when you retrieve codes, you find code 88, or code P1214 if the vehicle has the OBD-II system, which means the PCM/TCM has forgotten its top-dead-center settings.
Also, during the road test you lost 4th gear and lockup; this is the default action taken when a TDC Offset code is stored.
Figure 6 shows the TDC Offset relearn procedure for 1994-95 and 1996-and-later vehicles, and how to adjust the fuel-injection pump if necessary.
Keep in mind that a faulty injector pump or a faulty lift pump also can cause this problem.
One final note on this subject: Computer replacement also can cause the problems mentioned here and the need for some kind of relearn procedure, although in some cases all that’s needed is just to drive the vehicle.
Although some of these problems are not actual transmission problems, they do affect you, because “Tag, you’re it.”
Until next time.
Pete Luban is a technical consultant for the Automatic Transmission Service Group (ATSG) and a frequent contributor to Transmission Digest.