STREET SMART: A Silver Bullet A failure to identify the build
combination you’re working with may result in problems with line pressure, TCC operation or clutch apply or release.
• Shortening the pressure regulator valve train to make room for the input speed sensor wiring and connector.
• Updating the wiring harness for the input speed sensor.
• Adding DTCs for ISS diagnos- tics.
Turbine Shaft Design Variations Four non-ISS shaft sizes are
available: • 245mm/258mm shaft (P/N 17803688)
• 280mm/300mm shaft (P/N 17803687)
• 300mm HD/300mm M70 (P/N 17803686)
• 258mm PHT (P/N 17803685) Three ISS equipped shafts are
available: • 245mm/258mm (P/N 24232438) • 280mm/300mm (P/N 24230653) • 300mm HD/M70 (P/N 24230654)
So now that we’ve covered a little
background on the system, let’s take a look at this problem… and that silver bullet I promised.
Harsh Shifts; Code P0717 We first learned about this problem
from a tech call on a 2007 Suburban C1500 5.3L equipped with a 4L65E. The vehicle came into the shop with a complaint of a harsh shift and the Check Engine light on. So the first thing the technician did was hook up the scan
6
tool and check for codes. On this vehicle the only code was
DTC P0717 — Input Speed Sensor (ISS).
So his first step was to pull up the
diagnostic information for code P0717. What he got was six pages of circuit descriptions, conditions for running the DTC, conditions for setting the DTC, action taken when the DTC sets, condi- tions for clearing the DTC. Then he found 15 steps of diag-
nostic procedures for isolating and diagnosing code P0717. This is good until he reached step 5, number 2: “Connect the J 38522 variable sig-
nal generator to the AT ISS signal cir- cuit at the AT 20-way connector, engine harness side.” Honestly, how many of you have
the J 38522 variable signal generator? Unless you work for a dealership, the answer is, probably not many. The technician didn’t, and that’s where his problem began. Without the J 38522 variable sig-
nal generator, he couldn’t continue to follow the diagnostic procedure. This technician decided the next logical thing to do would be to replace the (ISS). The only drawback to that was the sensor is inside the transmission. The (ISS) assembly is a three-
wire, Hall Effect sensor that’s mounted inside the transmission on the oil pump assembly. The ISS gear meshes with
Figure 2
the gear teeth on the turbine shaft. To replace the ISS you have to remove the transmission and pump. So he did: He pulled the transmis-
sion, removed the pump, and replaced the ISS. Then he reassembled the trans- mission and reinstalled it into the vehi- cle. And then he took the vehicle out for a road test. On the road test the MIL came back on, code P0717 returned, and once again he had harsh shifts. This is where he called the ATRA
HotLine. My first question was, “How long
did it take for the code to set?” I waited while the technician cleared the code and started to drive the vehicle. That’s when I heard him say a very naughty word. “Now it’s not shifting at all! Wait, the Check Engine light came back on and it’s shifting again!” So I had him drive the vehicle
back to the shop to run some electrical checks.
About the ISS Signal The ISS signal is an input the TCM
uses to control line pressure, shift pat- terns, TCC slip speed, and gear ratio. When code P0717 sets, the TCM:
• commands maximum line pres- sure.
• freezes transmission adapts. • calculates a default ISS RPM.
GEARS March 2012
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