ZF 4 HP 16 AUTOMATIC TRANSAXLE 5A1 – 235

valves.
Valve Body S Assures limited operation of the automatic trans-
Valve body performs the following tasks: axle in the event of the electronics failing.
S Generates the line pressure needed for actuating S Actuating the lock–up clutch.
the shift elements. S Generating the lubricating pressure for the trans-
S Actuates the individual shift elements via the clutch axle

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ELECTRONICAL COMPONENTS Automatic Transaxle Output Speed Sensor

(A/T OSS)
Selector Lever/Program Switch The vehicle A/T OSS is a magnetic inductive pickup that
The driver engages the travel position via the selector le- relays information relative to vehicle speed to the TCM.
ver: Vehicle speed information is used by the TCM to control
shift timing, line pressure, and TCC (lock–up clutch) apply
P : Park Position
and release.
R : Reverse
N : Neutral The output speed sensor mounts in the case at the speed
D : Forward Speeds sensor rotor, which is pressed onto the spur gear. An air
gap of 0.1mm~1.3mm(0.004~0.05in) is maintained be-
Park/Neutral Position Switch tween the sensor and the teeth on the spur gear teeth. The
sensor consists of a permanent magnet surrounded by a
The Park/Neutral Position Switch is located on the selec-
coil of wire.
tor shaft and informs the TCM of the current selector lever
position P–R–N–D–3–2–1. As the differential rotates, an AC signal is generated by the
output speed sensor (OSS).
The selector lever position is transmitted to the TCM in en-
coded form along 4 lines. The encoding is such that mal-
functions in the connecting lead are identified.
The Park/Neutral Position Switch is located on the selec-
tor shaft, which is connected to the selector lever via a pull
cable. In addition, the Park/Neutral Position Switch con-
trols the starter interlock, the reversing light and the selec-
tor lever position indicator on the instrument panel.

Signal Combination

L1 L2 L3 L4
P 0 0 12 0
R 0 0 0 12
N 0 12 0 0 Automatic Transaxle Input Speed Sensor
D 12 12 12 0 (A/T ISS)
The A/T ISS is a magnetic inductive pickup that relays in-
3 12 12 0 12
formation relative to transaxle input speed to the TCM.
2 12 0 12 12 The TCM uses transaxle input speed information to con-
1 0 12 12 12 trol line pressure, TCC apply and release and transaxle
shift patterns. This information is also uses to calculate the
appropriate operating gear ratios and TCC slippage.
The input speed sensor mounts onto piston B that is inside
of valve body.
An air gap of 1.8~2.2mm(0.07~0.086inch) is maintained
between the sensor and the piston B.
The sensor consists of a permanent magnet surrounded
by a coil of wire. As the piston B is driven by the turbine
shaft, an AC signal induced in the input speed sensor.
Higher vehicle speeds induce a higher frequency and volt-
age measurement at the sensor.
Sensor resistance should measure between 825~835
ohms at 20°C (68°F). Sensor can measure from
1,000~8,000HZ.

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Line Pressure Resistance

Solenoid ON(low) 26.5 ± 0.5ohm
valve 1/Sole- 89.9~98.6 psi
noid valve 2 (6.2~6.8 bar)
OFF(high)
S 221.9~253.24
psi
S (15.3~17.46
bar)

Shift Solenoid Valve: Solenoid 1,2

The shift solenoids are two identical, normally open elec-
tronic exhaust work that control upshifts and downshifts in
all forward gear ranges. These shift solenoids valves to-
gether in a combination of ON and OFF sequences to con-
trol the line pressure and shift mechanisms (clutches,
brakes).
Pressure Control Solenoid Valve (EDS
Solenoid 1 controls the high or low of the line pressure VALVE 3,4,5,6)
(flow to each clutch valve) by the operation type (ON/
OFF), i.e. solenoid 1is ON, line pressure will be low The pressure control valve (EDS valve 3,4,5,6) is a preci-
(87~116 psi (6~8bar)), solenoid 1 is OFF, line pressure will sion electronic pressure regulator that controls the opera-
be high (232~261 psi (16~18bar)). tion of the clutches, brakes and the lock–up clutch.
The valve reduces the system pressure with which the
Solenoid 2 controls the oil flow to clutch valve E or lockup downstream solenoid valves and electrical pressure regu-
clutch valve by the ON/OFF signal. lating valves are supplied. It is possible to use smaller so-
lenoid valves as a result. The EDS require a constant input
The TCM monitors numerous inputs to determine the ap- pressure.
propriate solenoid state combination and transaxle gear
for the vehicle operating conditions.

Gear Solenoid 1 Solenoid 2

Park, Neutral ON ON
First ON/OFF ON
Second ON/OFF OFF
Third ON/OFF OFF
Fourth ON/OFF OFF
Reverse ON/OFF ON

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Transaxle Fluid Temperature (TFT) Sensor

The TFT sensor is a positive temperature coefficient
thermistor (temperature sensitive resistor) that provides
information to the TCM regarding transaxle fluid tempera-
ture. The temperature sensor is located in valve body. Cal-
culated temperature is a factor used to determine the shift
time and shift delay time.
The internal electrical resistance of the sensor varies in
relation to the operating temperature of the transaxle fluid
(see chart).

The TCM measures this voltage as another input to help

control line pressure, shift schedules and TCC apply.

When transaxle fluid temperature reaches 140°C (284°F)

the TCM enters ”hot mode.” Above this temperature the
TCM modifies transaxle shift schedules and TCC apply in
an attempt to reduce fluid temperature by reducing trans-
axle heat generation. During hot mode the TCM applies
the TCC at all times in fourth gear.
The TCM sends a 5 volt–reference signal to the tempera-
ture sensor and measures the voltage rise in the electrical Also, the TCM commands the 2–3 and 3–4 shifts earlier
circuit. A higher fluid temperature creates a higher resist- to help reduce fluid heat generation. Hot mode may not be
ance in the temperature sensor, thereby measuring a low- available on some applications.
er voltage signal.

Transaxle Sensor – Temperature To

Resistance To Voltage (approximate)
°C (°F) R high (ohms) R low (ohms) °C (°F) R high (ohms) R low (ohms)
–40 (–40) 586 556 50 (122) 1,206 1,173
–30 (–22) 641 611 60 (146) 1,295 1,256
–20 (–4) 699 670 70 (158) 1,388 1,341
–10 (14) 760 732 80 (176) 1,485 1,430
0 (32) 825 799 90 (194) 1,585 1,522
10 (50) 893 868 100 (212) 1,690 1,617
20 (68) 963 942 110 (230) 1,798 1,715
25 (77) 1,000 980 120 (248) 1,910 1,816
30 (86) 1,039 1,017 130 (266) 2,025 1,920
140 (284) 2,145 2,027

S Bent pins in the connector from rough handling dur-

Transaxle Electrical Connector ing connection and disconnection.
The transaxle electrical connector is a very important part S Wires backing away from the pins or coming un-
of the transaxle operating system. Any interference with clamped (in either internal or external wiring har-
the electrical connection can cause the transaxle to set ness).
Diagnostic Trouble Codes (DTCs) and/or affect proper op- S Dirt contamination entering the connector when dis-
eration. connected.
S Pins in the internal wiring connector backing out of
The following items can affect the electrical connections:
the connector or pushed out during reconnection.

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S Excessive transaxle fluid leaking into the connector, Carefully limit twisting or wiggling the connector during re-
wicking up into the external wiring harness, and moval. Bent pins can occur.
degrading the wire insulation. DO NOT pry the connector off with a screwdriver or other
S Water/moisture intrusion in the connector. tool.
S Low pin retention in the external connector from
excessive connection and disconnection of the wir- To reinstall the external wiring connector, first orient the
ing connector assembly. pins by lining up arrows on each half of the connector.
S Pin corrosion from contamination. Push the connector straight down into the transaxle with-
S Broken/cracked connector assembly. out twisting or angling the mating parts.
S Points to remember when working with transaxle The connector should click into place with a positive feel
wiring connector assembly. and/or noise.
S To remove the connector, squeeze the two tabs
towards each other and pull straight up (refer to Transaxle Control Module (TCM)
illustration). The transaxle control module (TCM) is an electronic de-
vice which monitors inputs to control various transaxle
functions including shift quality and transaxle sensors,
switches, and components to process for use within its’
control program. Based on this input information, the TCM
controls various transaxle output functions and devices.

Data Link Connector (DLC)

The data link connector (DLC) is a multiple cavity connec-
tor. The DLC provides the means to access serial data
from the TCM to aid in powertrain diagnosis. The DLC al-
lows the technician to use a scan tool to monitor various
systems and display diagnostic trouble codes (DTCs).
The DLC connector is located within the driver’s compart-
ment, directly below the steering column.

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