Isuzu Trooper (1998-2002 year). Service manual - part 793

TRANSMISSION CONTROL SYSTEM (4L30–E)

7A1–81

DTC P1850 Brake Band Apply Solenoid Malfunction

LHD

D07R200053

7A1–82 TRANSMISSION CONTROL SYSTEM (4L30–E)

RHD

D07R200054

Circuit Description

D

The brake band apply solenoid is a normally open
solenoid which controls the flow of fluid for brake band
application.  The Powertrain Control Module (PCM)
uses Pulse Width Modulation (PWM) and changes
the duty cycle to control the solenoid.  The PCM turns
the solenoid on (energized) and off (deenergized) at a
constant frequency.  The length of time the solenoid is
energized during each on/off cycle is called the pulse
width.  By varying or “modulating” the pulse width, the
solenoid output pressure is changed.  Since the
solenoid is normally open, increasing the pulse width
increases the duty cycle and decreases the output
pressure.  PWM control provides smooth band
application without an accumulator.  The band is only
applied in first and second gears.

D

In the event of an electrical failure (open), the
solenoid regulates at the maximum oil flow (0% duty
cycle).

D

The solenoid is activated by current.  This current is
produced by applying a voltage to one side (the High
side) and a ground to the other side (Low side).

D

The High Side Driver (HSD) is a circuit of the PCM
that acts as a switch between the solenoids and the
supply voltage.  The High side of the solenoid is
permanently supplied with voltage. When the ignition
is off, the HSD is turned off.

This DTC detects a continuous open or short to ground in
the brake band apply solenoid circuit or the brake band
apply solenoid.  This is a type “D” DTC.

Conditions For Setting The DTC

D

Battery voltage is between 10 and 16 volts.

D

Ignition is “on”, Engine “run”.

D

The PCM commands the solenoid “on” and the
voltage remains high (B+) or the PCM commands the
solenoid “off” and the voltage remains low (zero
volts).

D

All conditions met in 1.34 

∼

 1.56 seconds.

Action Taken When The DTC Sets

D

Inhibit brake band apply solenoid.

D

The PCM will not illuminate the Malfunction Indicator
Lamp (MIL).

Conditions For Clearing The DTC

D

The DTC can be cleared from the PCM history by
using a scan tool.  

D

The DTC will be cleared from history when the vehicle
has achieved 40 warmup cycles without a failure
reported.

D

The PCM will cancel the DTC default actions when
the fault no longer exists and the ignition is cycled “off”
long enough to power down the PCM.

TRANSMISSION CONTROL SYSTEM (4L30–E)

7A1–83

Diagnostic Aids

D

Inspect the wiring for poor electrical connection at the
PCM and at the transmission 16–way connectors.
Look for possible bent, backed out, deformed or
damaged terminals.  Check for weak terminal tension
as well.  Also check for a chafed wire that could short
to bare metal or other wiring.  Inspect for a broken wire
inside the insulation.

D

When diagnosing for a possible intermittent short or
open condition, move the wiring harness while
observing test equipment for a change.

Test Description

The numbers below refer to the step numbers on the
diagnostic chart:
3. This test checks for power to the brake band apply

solenoid from the ignition through the PCM.

4. This test checks the resistance of the transmission

internal wiring harness and brake band apply
solenoid.

5. This test checks the ability of the PCM and wiring to

control the ground circuit.

DTC P1850 Brake Band Apply Solenoid Malfunction 

Step

Action

Yes

No

1

Were you sent here from the “Powertrain On–Board Diagnostic
(OBD) System Check”?

Go to Step 2

Go to OBD

System Check

Refer to

Driveability and

Emissions in

Engine section

2

1. Install the scan tool.
2. With the engine “on”, turn the ignition switch “on”.

NOTE: Before clearing DTC(s), use the scan tool to record “Freeze
Frame” and “Failure Records” for reference, as data will be lost
when the “Clear Info” function is used.

3. Record the DTC “Freeze Frame” and “Failure Records”.

Were DTCs P0753, P0758 set?

Go to Step 3

Go to Step 4

3

Using the J39200 DVOM, back probe between PCM connector
terminals S–43 and F–1.

Is the voltage between 10 to 12 volts?

Go to Step 5

Go to Step 6

4

1. Turn the ignition “off”.
2. Disconnect the F (BLUE) and S (RED) PCM connectors.
3. Using the J39200 DVOM, measure the resistance between

PCM connector terminals S–43 and S–10.

Is the resistance within 10–12 ohms?

Go to Step 12

Go to Step 13

5

Using the J39200 DVOM, back probe between PCM connector
terminals S–10 and F–1.

Is the voltage between 10 to 12 volts?

Go to Step 26

Go to Step 4

6

1. Turn the ignition “off”.
2. Disconnect the F (BLUE) and S (RED) PCM connectors.
3. Using the J39200 DVOM, check continuity between PCM

terminal S–43 and ground.

Is there a continuity?

Go to Step 7

Go to Step 9

7

1. Disconnect the transmission 16–way connector H–69.
2. Using the J39200 DVOM, check continuity between connector

H69–9 (LHD) or H69–12 (RHD) and ground.

Is there a continuity?

Go to Step 8

Go to Step 17

8

1. Disconnect the transmission main case connector M–7.
2. Using the J39200 DVOM, check continuity between the

terminal M7–7(B) and ground.

Is there a continuity?

Go to Step 18

Go to Step 19

7A1–84 TRANSMISSION CONTROL SYSTEM (4L30–E)

DTC P1850 Brake Band Apply Solenoid Malfunction  (Cont’d)

Step

No

Yes

Action

9

1. Disconnect the F (BLUE) and S (RED) PCM Connector.
2. Using the J39200 DVOM, measure the resistance between

PCM connector terminals S–43 and S–10.

Is the resistance within 10–12 ohms?

Go to Step 26

Go to Step 10

10

1. Disconnect the transmission 16–way connector H–69.
2. Using the J39200 DVOM, measure the resistance between

terminal H69–11 and H69–9 (LHD), or H69–10 and H69–12
(RHD).

Is the resistance within 10–12 ohms?

Go to Step 17

Go to Step 11

11

1. Disconnect the transmission main case connector M–7.
2. Using the J39200 DVOM, measure the resistance between

terminals M7–2(D) and M7–7(B).

Is the resistance within 10–12 ohms?

Go to Step 20

Go to Step 21

12

Using the J39200 DVOM, check continuity between PCM
terminal S–10 and ground.

Is there a continuity?

Go to Step 14

Go to Step 26

13

1. Disconnect the transmission 16–way connector H–69.
2. Using the J39200 DVOM, measure the resistance between

terminal H69–11 and H69–9 (LHD), or H69–10 and H69–12
(RHD).

Is the resistance within 10–12 ohms?

Go to Step 24

Go to Step 15

14

1. Disconnect the transmission 16–way connector H–69.
2. Using the J39200 DVOM, check continuity between terminal

H69–9 (LHD) or H69–12 (RHD) and ground.

Is there a continuity?

Go to Step 16

Go to Step 22

15

1. Disconnect the transmission main case connector M–7.
2. Using the J39200 DVOM, measure the resistance between

terminals M7–2(D) and M7–7(B).

Is the resistance within 10–12 ohms?

Go to Step 25

Go to Step 21

16

1. Disconnect the transmission main case connector M–7.
2. Using the J39200 DVOM, check continuity between the

terminal M7–7(B) and ground.

Is there a continuity?

Go to Step 18

Go to Step 23

17

The wiring harness between PCM terminal S–43 and
transmission 16–way connector terminal H69–11 (LHD), or
H69–10 (RHD) is open.

Was a problem found and corrected?

Go to Step 27

—

18

The brake band apply solenoid is faulty, or the internal wiring
harness from the brake band apply solenoid is shorted to ground.

Was a problem found and corrected?

Go to Step 27

—

19

The wiring harness between the transmission 16–way connector
terminal H69–11 (LHD) or H69–10 (RHD) and the transmission
main case connector terminal M7–2(D) is shorted to ground.

Was a problem found and corrected?

Go to Step 27

—

20

The wiring harness between the transmission 16–way connector
terminal H69–11 (LHD) or H69–10 (RHD) and the transmission
main case connector terminal M7–2(D) is open.

Was a problem found and corrected?

Go to Step 27

—