Done in a flash

Faced with a persistent vehicle defect for which you have thoroughly understood, tested and inspected and still come up empty? Flash programming the involved ECU is something that you may want to try.

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ost manufacturers will generate TSBs stating defects that flash programming will correct. These programming files have updated calibration numbers to reflect the corrected software. However, there are some defects that are corrected by flash programming even though the calibration files may be the same number as the one already loaded in the ECU. These defects may or may not be listed in any TSB nor listed anywhere else officially by the OEM for that matter. I won’t speculate why this is the case, however, from experience I know darn well it is. Let’s take a look at a few examples of defects known to be corrected by simply flashing the ECU with the same calibration number.

Our first case is one for which there actually is a TSB (GM PIP#4578) stating to flash with the same calibration number. A shop replaced the electronic throttle body assembly on a 2005 GMC Envoy. After replacement the PCM set a persistent P0507 idle speed error DTC. Performing an idle relearn procedure with a competent scan tool did not correct the concern. However you can see in Figure 1 that after reprogramming the PCM the Desired Idle speed PID now matches the Actual Idle speed PID on this brand new throttle body.

GM vehicles seem to suffer a number of DTCs that are only corrected with non-documented flashes of the PCM. The first ones I ran into were 3.1L and 3.8L engines that set a DTC P0401 for EGR insufficient flow. The shop typically replaced the EGR valve, checked all circuitry and bidirectional control functions and removed the intake manifold to clean all EGR ports, only to have the DTC come back. Flashing the PCM on these vehicles, many with the same calibration number, fixes the low flow DTC test failure.Another common defect is the GM 4.3L engines setting false misfire DTCs. Typically two cylinders will register constant misfires evenly at any RPM range. Yet the engine is not actually felt to be misfiring. When a crankshaft variation learn procedure is attempted to correct the learned bad misfire identification the learn procedure will be locked out because the PCM thinks the engine is currently misfiring. Flashing the PCM with the same or newer calibration file seems to remove the false misfires and allows a successful running of the crankshaft variation learn. This defect seems to occur when the distributor is being removed/replaced or the battery is changed.

Yet another GM EGR system defect is that of a “Closed valve position error” DTC being set after an EGR valve replacement or repair of a circuit defect during which the PCM has learned a new, lower, EGR closed valve position. After repairs are made the PCM will not learn the new correct closed valve position. This causes an expected EGR Position Error DTC. Cycling the key or disconnecting the battery is supposed to enable a new closed valve position to be learned but on some 3.8L engines it will not. Flashing the PCM will force the PCM to learn the new EGR closed valve position value.

At times an existing ECU calibration or variant coding can get corrupted due to outside influences and must be re-flashed. The opening screen of Chryslers wiTECH scan tool software seen here in Figure 2 is showing all the ECUs lit up in gold indicating these ECUs have DTCs set in them. You can also see in the bottom of figure 2 that both Low Battery Voltage and VIN Mismatch DTCs have been set in some ECUs. However the VIN shown in the upper left of this screen is correct for this vehicle. Further investigation shown in Figure 3 indicates that only the PCM had the incorrect VIN stored. After rewriting the VIN to the PCM all the ECU DTCs cleared. On this particular 2006 Jeep the customer had jumped started the vehicle for some reason. This is the second time I have seen jump starting the battery cause a corruption of ECU VIN calibration on several Chrysler products.

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