TRNSMISSION THERPY When diagnosing a transmission electrical problem, it s often necessary to monitor signals by back-probing the computer connector. However, 1990-93 Troopers and 1991-93 Rodeos make this task very difficult for two reasons. First, the connector looks as though it s impossible to back-probe (figure 1). Second, once you access the connector, you soon learn that there are absolutely no voltage specifications available...anyby Larry Frash The 4L30E Files: Figure 1 The computer connector looks impossible to back-probe. Remove this screw that holds the shield to the connector shield Figure 2 Figure 3 Remove tape from rubber boot 26 GERS ugust 2003
where. This lack of information makes it very difficult to diagnose these vehicles. Even though these vehicles are over 10 years old, something had to be done. In this edition of Transmission Therapy, we ll show you how to access the computer connector and supply you with the voltage specifications. This information is often useful when diagnosing trouble codes and driveability problems. Then we ll cover code retrieval and focus on the most common solenoid codes. ack-probing the omputer The first step when trying to backprobe the computer connector is to locate the computer: Look for it behind the driver s side of the dash, to the left of the steering column. Then follow these easy steps: Unbolt the transmission computer from its bracket. isconnect the computer and remove the screw that holds the shield to the connector (figure 2). Remove the tape from the rubber boot (figure 3) and slide the shield up the harness and away from the connector (figure 4). Once you have the shield removed, plug the connector back into the computer (figure 5). That solves the first problem: Now you can back-probe the computer connector. Figure 6 shows the computer connector as viewed from the wire side. Figure 7 (page 30), lists the function of each pin, with the correct voltage values. ode Retrieval 90-91 Look for a two pin diagnostic connector, located under the dash, behind the hood release. Ground the wire that is yellow with a black stripe. 92-93 Look for a three pin diagnostic connector, located under the dash to the left of the center console. Ground the wire that is yellow with a black stripe. Some of these connectors are hard to find and often rest next to similarlooking connectors. If you can t find the diagnostic connector or aren t sure which one to use, you can simply ground pin 25 at the computer connector on all 1990-93 models. Reading Trouble odes The heck Trans light will flash the codes. The first set of flashes indicate the tens digits, a short pause and then the ones digits. For example, to display a code 43, the computer would flash the heck Trans light four times, a short pause, then flash three more times. The computer will repeat each code three times, with a long pause between each code. Even without any problems, the first code will always be a code 12. This simply means that the computer is in diagnostic mode. See figure 8 (page 32), for a complete code list. 1-2/3-4, 2-3 & and pply Solenoids system tests We ll call these three solenoids the main case solenoids. uring initial start-up, the computer runs the solenoid circuits through a series of tests. The main case solenoids must pass all three tests. Test one: The computer checks for a short to ground on pins 43, 45 and 48 (figure 9, page 32). If there is a short to ground on any of these three circuits, the computer will set solenoid shorted to ground codes (17, 26 and/or 35), turn off all three solenoid drivers (transistors in the computer) and stop testing. This will cause the transmission to be in failsafe. If all three circuits pass this test, the computer will go to test two. Test two: The main case solenoids are supplied ground from the computer through what we ll call the ground relay, located inside the computer (figure 10, page 32). efore the computer turns the ground relay on, it monitors the solenoid side of the relay by pulsing the three main case solenoid drivers on GERS ugust 2003 27
The 4L30E Files: E-LSSIFIE and off several times. Since the relay is open, the computer expects to see the voltage alternate 0-12-0-12 on pin 54 (figure 11, page 32). If the computer only sees 12 volts (figure 12, page 34), it knows there is either a short to + or one of the solenoid drivers is stuck on. If the computer only sees zero volts on pin 54 (figure 13, page 34), it knows that either the circuit is shorted to ground, has an open in all three solenoids or all three solenoid drivers are stuck off. In either of these situations, the computer will set a code 43 and not turn the relay on. Once a code 43 is set the computer will also turn all three solenoid drivers off and stop testing. Keep in mind, the computer only pulses the solenoids for about 0.25 seconds during this test and is best seen with an LE or an oscilloscope. If the ground relay passes this test, the relay is turned on and supplies ground to the three main case solenoids allowing test three to begin. Note: ecause the computer stops monitoring the ground circuit once the relay is turned on, a code 43 will not set after the initial test is complete, even if there is an intermittent open in the ground circuit. connector Figure 4 Slide the shield up the harness and away from the connector Test three: Once the ground relay is closed and supplies ground to the main case solenoids, the computer can check for open circuits and shorts to + on pins 43, 45 and 48 (figure 14, page 34). If there are, the computer will set solenoid codes for open or shorted to + (25, 28 and/or 34) and turn all three solenoid drivers off. Keep in mind, if the ground relay contacts are burnt, the computer will think there is an open in all three main case solenoids. However, because the computer only monitors the solenoid side of the ground relay (pin 54), it will not set a code 43 even though the ground relay is bad. uring normal operation, the computer is constantly checking for shorts to ground, open circuits and shorts to + on pins 43, 45 and 48. If any main case solenoid code is set, the computer will turn all three solenoid drivers off and turn off the ground relay. Once you have removed the shield, plug the connector back into the computer. Figure 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 onnector viewed from the wire side. Figure 6 iagnosis To diagnose any main case solenoid codes including code 43, disconnect the computer. With the key on, engine off, check for positive voltage on pins 43, 45, 48 and 54 and then 28 GERS ugust 2003
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The 4L30E Files: E-LSSIFIE 90-93 Isuzu Trooper/91-93 Rodeo Pin harts PinFunction ondition Signal 1 / Request off 0 V on + 2 ruise ontrol 3 N/ - - 4 N/ - - 5 N/ - - 6 TPS Idle 0.5 V Full Throttle 4.5 V 7 Power Mode Indicator Not in Power Mode (Light Off) + In Power Mode (Light On) 0 V 8 Range Selector Pin Manual P, R & N 0 V Manual, 3, 2 & L + 9 N/ - - 10 Winter Mode Indicator Not in Winter Mode (Light Off) + In Winter Mode (Light On) 0 V 11 Engine RPM 91-92 Frequency varies with Rodeo, 90-91 Trooper engine rpm 12 N/ - - 13 iagnostic - - 14 VSS Ground lways < 0.10 V 15 Kickdown Switch ll Except Full Throttle + Full Throttle 0 V 16 Ground lways < 0.10 V 17 Ground lways < 0.10 V 18 Ground lways < 0.10 V 19 Ground lways < 0.10 V 20 VSS Signal Vehicle Stopped 0 V Vehicle Moving > 0.5 V 21 / ut Relay 22 Fluid Temp 32 F (0 ) 4.4 V 68 F (20 ) 3.6 V 176 F (80 ) 1.0 V 248 F (120 ) 0.4 V 23 Range Selector Pin Manual N, & L 0 V Manual P, R,3 & 2 + 24 5 V Reference Voltage Key Off 0 V Key On 5 V 25 iagnostic Enable Normal + uring ode Retrieval 0 V 26 Range Selector Pin Manual P, 2 & L 0 V Manual R, N, & 3 + 27 N/ - - 28 Keep live Power lways + 29 heck Trans Indicator heck Trans Light Off + heck Trans Light On 0 V PinFunction ondition Signal 30 oolant Temp Engine Temp old + Engine Temp Warm 0 V 31 Winter Mode Switch Switch Released + Switch epressed 0 V 32 N/ - - 33 Range Selector Pin G Manual R, & 2 0 V Manual P, N,3 & L + 34 Power Mode Switch Switch Released + Switch epressed 0 V 35 N/ - - 36 Ground lways < 0.10 V 37 Ignition Key Off 0 V Key On + 38 T Solenoid Lockup Off 0 V Lockup On + 39 rake Switch rake Pedal Released + rake Pedal epressed 0 V 40 Force Motor High Minimum Pressure 1.0 mp Maximum Pressure 0.1 mp 41 Force Motor Low Minimum Pressure 1.0 mp Maximum Pressure 0.1 mp 42 N/ - - 43 enoid Solenoid Off 0 V Solenoid On + 44 N/ - - 45 and pply Solenoid Not ctive 0% duty ctive pprox 51% 46 N/ - - 47 N/ - - 48 1-2 / 3-4 Solenoid Solenoid Off 0 V Solenoid On + 49 N/ - - 50 arometric Sensor (Some Models) 51 N/ - - 52 N/ - - 53 Reference Voltage Key Off 0 V Key On 5 V 54 Solenoid Ground Normal Operation 0 V W/code 43, 17, 25, 26, 28, 34 or 35 + 55 Engine RPM Frequency varies with 93 Rodeo, engine rpm 92-93 Trooper Figure 7 30 GERS ugust 2003
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The 4L30E Files: E-LSSIFIE Trouble odes 17 1-2/3-4 Shift Solenoid shorted to ground 21 TPS voltage too high (above 4.9V) 22 TPS voltage too low (below 0.06V) 23 Engine oolant Switch voltage too high. Note: ode will set if engine is not at operating temperature after 20 minutes running time. 25 1-2/3-4 Shift Solenoid open or shorted to + 26 2-3 Shift Solenoid shorted to ground 28 2-3 Shift Solenoid open or shorted to + 29 T Solenoid shorted to ground 31 No Engine RPM signal (no signal above 19 mph with TPS above 12%) 32 Force Motor circuit open (current less than 0.095) 33 Force Motor circuit shorted to + (current higher than 1.5) 34 and pply Solenoid open or shorted to + 35 and pply Solenoid shorted to ground 36 T Solenoid open or shorted to + 39 No VSS signal 41 Gear Ratio Error 43 Ground ontrol ircuit open, shorted to ground or shorted to + 46 own Shift Error 48 Low attery Voltage (below 9.0V at TM pin 37) 49 High attery Voltage (above 16V at TM pin 37) 55 EPROM Failure (bad computer) 56 Mode Switch input incorrect 65 Transmission Temp Sensor circuit open 66 Transmission Temp Sensor circuit shorted to ground 77 Kickdown Switch shorted to ground (stuck closed) 82 Mode Switch input incorrect The computer checks for shorts to ground on Pins 43, 45 and 48 PU PU Ground Relay Open Ground Relay Open The computer pulses battery voltage (+) to pins 43, 45 and 48 and monitors these pulses on pin 54. PU and pply Sol Main ase onnector System Test 1 and pply Sol Main ase onnector The ground relay supplies a constant ground to the solenoids only if the system passes all tests. and pply Sol System Test 2 System Test 2 continued Figure 9 Figure 10 Figure 8 check for continuity to chassis ground on the same pins. There should be no voltage and no ground on either of these pins. If there is, use the wire diagram in figure 9 to re-wire the circuit that failed this test from the computer to Ground Relay Open the main case solenoids. Next, check the resistance of each of the main case solenoids using the Main ase onnector chart in figure 15, page 38. If one or more of these circuits failed this test, you either have a bad solenoid or a bad Figure 11 32 GERS ugust 2003
The 4L30E Files: E-LSSIFIE and pply Sol System Test 2 continued The computer only needs to see the voltage pulse from one of the main case sole- PU noids, so testing this circuit is actually simple. PU Ground Relay Open and pply Sol Main ase onnector System Test 2 continued If the computer sees zero volts all the time during this test, it knows there is either a short to ground, open in all three solenoids or all three solenoid drivers are stuck off. Figure 13 PU Ground Relay Open Ground Relay Open Main ase onnector If the computer sees + on pin 54 all the time during this test, it knows there is either a short to + or one of the solenoid drivers are stuck on. and pply Sol Main ase onnector System Test 3 Figure 12 If system tests 1 and 2 pass, the ground relay is closed and supplies a constant ground to the solenoids. Once the relay is closed, the computer begins test 3 to check for open circuits and shorts to +. Figure 14 connection between the computer and the solenoid. Re-wire and/or replace the solenoid in the circuit that failed the test as necessary. You may also have a problem in the ground wire between pin 54 and the main case solenoids, or the ground relay contacts are burnt. If there is no voltage and no ground on these pins, and the solenoid resistance readings are correct, there is a good chance that these codes are being caused by a bad computer. Use the following tests to rule out a bad computer. ode 43 (Solenoid ground circuit) The computer only needs to see the voltage pulse from one of the main case solenoids, so testing this circuit is actually simple. lear any codes by disconnecting the computer. ut the wires on pins 48 and 54 approximately one inch from the computer connector. onnect the two wires from the computer through a 27 ohm/25 watt resistor. Plug the computer connector into the computer, turn the key on and check codes. If code 43 is set, the computer is bad. If code 43 does not set, something was overlooked during the initial testing of the circuit. odes 26 and/or 28 (2-3 solenoid codes) lear codes by disconnecting the computer. ut the wire on pin 43 approximately one inch from the computer connector. Splice pin 43 from the computer into the wire at pin 54 through a 27 ohm/25 watt resistor (figure 16, page 38). Plug the computer connector into the computer, turn the key on and check codes. If codes 26 and/or 28 are set, the computer is bad. 34 GERS ugust 2003
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The 4L30E Files: E-LSSIFIE Main case solenoid resistance chart Figure 15 omputer Pins Solenoid Resistance onnect ohm meter between pins 43 & 54 2-3 Shift Solenoid 17-24 ohms onnect ohm meter between pins 45 & 54 and pply Solenoid 9-14 ohms onnect ohm meter between pins 48 & 54 1-2/3-4 Shift Solenoid 17-24 ohms ut pin 43 approximately one inch from the computer connector. omputer Splice pin 43 into the wire at pin 54 through a 27 ohm/25 watt resistor. Figure 16 ut pin 45 approximately one inch from the computer connector. and pply Sol omputer Splice pin 43 into the wire at pin 54 through a 27 ohm/25 watt resistor. Figure 17 ut pin 48 approximately one inch from the computer connector. omputer Splice pin 43 into the wire at pin 54 through a 27 ohm/25 watt resistor. Figure 18 38 GERS ugust 2003
If codes 26 and/or 28 do not set, something was overlooked during the initial testing of the circuit. odes 34 and/or 35 (and apply solenoid codes) lear codes by disconnecting the computer. ut the wire on pin 45 approximately one inch from the computer connector. Splice pin 45 from the computer into the wire at pin 54 through a 27 ohm/25 watt resistor (figure 17). Plug the computer connector into the computer, turn the key on and check codes. If codes 34 and/or 35 are set, the computer is bad. If codes 34 and/or 35 do not set, something was overlooked during the initial testing of the circuit. odes 17 and/or 25 (1-2/3-4 solenoid codes) lear codes by disconnecting the computer. ut the wire on pin 48 approximately one inch from the computer connector. Splice pin 48 from the computer into the wire at pin 54 through a 27 ohm/25 watt resistor (figure 18). Plug the computer connector into the computer, turn the key on and check codes. If codes 17 and/or 25 are set, the computer is bad. If codes 17 and/or 25 do not set, something was overlooked during the initial testing of the circuit. ecause the computer has three separate tests for the main case solenoids and because it stops testing at the first sign of trouble, don t be surprised if different codes are set after you successfully repair the original ones. This also makes it very important to clear codes after each repair. odes are easily cleared by disconnecting the computer. Remember to always turn the key off when disconnecting and connecting any computer. Isuzu has created some interesting diagnostic dilemmas for technicians. ut if you stick to a careful diagnostic strategy, you should have no problem getting these vehicles out of your service bays and back on the road. GERS ugust 2003 39