Automatic Transmission Diagnosis - with Codes Land Rover Discovery L318

APPLICATION

Note. Automatic transmission will also be referred to as gearbox, and Electronic Automatic Transmission Electronic Control Unit (EAT ECU) will also be referred to as Transmission Control Module (TCM).

AUTOMATIC TRANSMISSION APPLICATIONS

IDENTIFICATION

The automatic transmission number is stamped on a plate attached to left side of automatic transmission casing, adjacent to gear selector. (Scheme 1)

Scheme 1

GENERAL

The automatic transmission is a 4-speed unit with electronic control of gear selection, shift quality and torque converter lock-up. Selections on the gear selector lever assembly are transmitted to the automatic transmission by a gear selector cable. A gear position switch on the automatic transmission transmits the gear selection to an Electronic Automatic Transmission Electronic Control Unit (EAT ECU), which outputs the appropriate control signals to an electro-hydraulic valve block in the automatic transmission. A mode switch enables the driver to change the control mode of the EAT ECU. The EAT ECU operates warning lamps in the instrument cluster to indicate the control mode and system status.

The automatic transmission features a pressure lubrication system and is cooled by pumping the lubricant through an engine oil cooler.

On 2003 vehicles, the ZF4HP24 transmission was introduced for use with the 4.6L V8 engine. This transmission is required to accommodate the increased power output of the larger engine. The ZF4HP22 transmission remains in use on vehicles with 4.0L V8 engines.

Both transmission units are of similar construction, with the ZF4HP24 unit being 0.6" (15 mm) longer than the ZF4HP22 unit to accommodate a larger transmission fluid pump. The operation of both transmission units is the same.

The gear change points of an electronically/hydraulically controlled transmission are more precise and consistent. With mechanical/hydraulic control there is a greater tolerance band regarding the gear change points because of the nature of mechanical components, which are influenced by conditions such as temperature and component wear.

The load on the transmission can be reduced by introducing engine intervention when the automatic transmission changes gear. Rather than operating independently of the engine management system, the transmission EAT ECU is capable of communicating with the Engine Control Module (ECM).

The automatic transmission consists of a torque converter housing, an intermediate plate, a automatic transmission housing and a rear extension housing, bolted together in series. (Scheme 2) The rear of the automatic transmission is supported by a rubber mounting installed between a mounting bracket on the automatic transmission and the left chassis rail. (Scheme 3) A heat shield is installed on the mounting to protect it from the exhaust.

Scheme 2

Scheme 3

Torque Converter Housing

The torque converter housing attaches the automatic transmission to the engine and contains the torque converter. The torque converter is connected to the engine drive plate and transmits the drive from the engine to the automatic transmission input shaft. When engaged, a hydraulic lock-up clutch in the torque converter prevents slippage, to give a direct drive from the engine to the automatic transmission for improved driving response.

Intermediate Plate

The intermediate plate supports the automatic transmission input shaft and provides the interface between the transmission fluid pump and the lubrication circuit. The pump attaches to the front of the intermediate plate and is driven by the impeller in the torque converter. The pump pressurizes transmission fluid drawn from the sump on the automatic transmission housing. The pressurized transmission fluid then circulates through the torque converter and automatic transmission housing components for cooling, lubrication and gear shift purposes. Ports around the outer periphery of the intermediate plate provide the inlet and outlet connections to the transmission fluid cooler and a pressure take-off point for servicing.

Automatic Transmission Housing

The automatic transmission housing contains 2 planetary gear sets on input and output shafts. Hydraulic brake clutches on the shafts control which elements of the gear sets are engaged and their direction of rotation, to produce the P and N selections, 4 forward gear ratios and one reverse gear ratio.

Valve Block

The lock-up and brake clutches are operated by pressurized transmission fluid from the valve block in the sump. A manual valve and 4 solenoid valves, also known as Motorized Valves (MV), control the supply of pressurized transmission fluid from the valve block

1. The manual valve controls the supply in P, R, N and D.
2. Solenoid valves MV1 and MV2 control the supplies that operate the brake clutches for shift control.
3. Solenoid valve MV3 controls the supply that operates the lock-up clutch.
4. Solenoid valve MV4 modulates the pressure of the supplies to the brake clutches, to control shift quality.

Operation of the manual valve is controlled by the gear selector lever assembly. In the automatic transmission, a selector shaft engages with the manual valve. The selector shaft also operates a mechanism that locks the output shaft when P is selected.

Operation of the solenoid valves is controlled by the Electronic Automatic Transmission Electronic Control Unit (EAT ECU).

An output shaft speed sensor in the automatic transmission housing outputs a signal to the EAT ECU. The EAT ECU compares output shaft speed with engine speed to determine the engaged gear, and output shaft speed with vehicle speed to confirm the range selected on the transfer box.

A bayonet lock electrical connector in the automatic transmission casing, to the rear of the gear selector lever, connects the solenoid valves and the output shaft speed sensor to the vehicle wiring.

A pressed steel sump encloses the valve block and collects transmission fluid draining from the automatic transmission housing. A suction pipe and filter on the underside of the valve block connect to the inlet side of the transmission fluid pump. A magnet is installed in the sump to collect any magnetic particles that may be present. A level plug and a drain plug are installed in the sump for servicing.

Rear Extension Housing

The rear extension housing provides the interface between the automatic transmission housing and the transfer box. A splined extension shaft, secured to the automatic transmission output shaft by a bolt, transmits the drive from the automatic transmission to the transfer box. A seal in the rear of the housing prevents leakage past the extension shaft. A breather pipe, attached to the left side of the rear extension housing, ventilates the interior of the automatic transmission and rear extension housings to atmosphere. The open end of the breather pipe is located in the engine compartment at the right front corner of the engine sump on automatic transmissions to early vehicles and is clipped to the top of the automatic transmission on late vehicles. (Scheme 2)

Automatic Transmission Power Flows

The following schematics show the power flow through the automatic transmission for each forward gear when "D" is selected, and for reverse. (Scheme 4)- (Scheme 8). The key to the item numbers on the schematics, and in parenthesis in the accompanying text, can be found on cutaway view of automatic transmission. (Scheme 9)

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Scheme 9

ELECTRONIC AUTOMATIC TRANSMISSION ELECTRONIC CONTROL UNIT

The Electronic Automatic Transmission Electronic Control Unit (EAT ECU) operates the solenoid valves in the automatic transmission to provide automatic control of gear shifts and torque converter lock-up. The EAT ECU is attached to a protective bracket which is secured to the cabin floor below the left front seat. A 55-pin connector links the EAT ECU to the vehicle wiring.

Using information from the Engine Control Module (ECM), together with its own sensors, the EAT ECU selects the most suitable gear. The gear selected depends on road speed (from output shaft sensor), throttle angle (from engine management), engine torque (from engine management), altitude (from engine management), and selector position (from gear position switch). (Scheme 10)

Other factors such as vehicle acceleration are also taken into account when the optimum gear is calculated.

The EAT ECU controls gear selection by directing pressurized transmission fluid to the required clutch assembly. This is achieved by controlling the operation of 2 shift solenoids incorporated within the valve block.

To enhance the quality of the gear changes, the EAT ECU sends a torque reduction signal to the ECM during gear changes. Responding to this signal, the engine management ECM will reduce engine torque, by retarding ignition timing, to improve shift quality.

Software in the EAT ECU monitors hard wired inputs and exchanges information with the ECM on a Controller Area Network (CAN) bus to determine gear shift and torque converter lock-up requirements. Resultant control signals are then output to the automatic transmission solenoid valves.

The CAN bus, introduced on 1999 model year gas vehicles, provides the communication link between ECM and TCM. Inputs and outputs to and from each control module are transmitted via 2 twisted wire connections, CAN high and CAN low. CAN bus allows more engine data to be passed to TCM which, on earlier vehicles, would require a number of additional hard wired connections. Additional engine data is used by TCM to give improved transmission quality and allows TCM to operate in a greater number of default modes in the event of sensor failure. Inputs and outputs on CAN communication bus are listed as follows. Inputs from ECM

1. Can Version Identifier
2. Emissions (OBD-II) Control
3. Engine IAT
4. Engine Speed
5. Engine Speed Fault Flag
6. ECT Sensor
7. Engine Torque
8. Engine Torque Fault Flag
9. Friction Torque
10. Maximum Engine Torque
11. Reduced Engine Torque
12. Road Speed
13. Status of engine speed torque reduction.
14. Throttle Position

Outputs to ECM

1. Calculated Gear
2. Diagnostic Information
3. Emission (OBD-II) Fault Status
4. Engine torque reduction request.
5. Gear position switch information.
6. Output Shaft Speed
7. Mode Information
8. Shift Information
9. TCC Lock-Up Solenoid

If during a jump start, normal operating voltage is exceeded, transmission will be set to limp home mode and output for solenoid valve and pressure regulator will be switched off. Normal EAT ECU operating volage is 9.0-16.0 volts. The EAT ECU can withstand an overcharge of 16.0-24.0 volts for one minute at 104 F° (40 C°) and a negative charge of down to -14 volts for one minute at 77 F° (25 C°) without sustaining damage. If voltage happens to drop to 6.5-9.0 volts, EAT ECU will run diagnostic checks on itself and CAN-Bus communication system. Also at this voltage, output for solenoid valves and pressure regulator will be switched off. At 3.0-6.5 volts EAT ECU will still retain data, but communication over CAN-Bus line will become unreliable and limp home mode will be activated. At 3.0 volts and under, system will not function.

Scheme 10

GEAR POSITION SWITCH

The gear position switch has 4 input lines known as the W, X, Y, and Z lines. The gear position switch provides the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) with the current driver-selected gear position. By analyzing the status of these inputs, the EAT ECU calculates which gear is most suitable for the current conditions.

Unlike the Range Rover model, Discovery uses a fourth gear position switch input line for improved electrical diagnostics and better lever position information (intermediate gear lever positions, i.e. to detect when the gear lever is moving between positions). This helps to align mechanical and electrical tolerances. The switch is installed on the selector shaft on the left side of the automatic transmission. Slotted mounting holes allow the switch to be turned relative to the shaft for adjustment. A fly lead connects the switch to the vehicle wiring.

Movement of the gear selector lever assembly turns the selector shaft, which operates 6 pairs of contacts in the switch. The pairs of contacts are identified as the W, X, Y, Z, Park/Neutral and Reverse contacts. When closed

1. The W, X, Y and Z contacts output a 12-volt ignition supply from the Body Control Unit (BCU).
2. The Park/Neutral contacts output an ground.
3. The Reverse contacts output a 12-volt ignition supply from the passenger compartment fuse box.

The outputs of the W, X, Y and Z contacts are monitored by the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) and the BCU to determine the position of the gear selector lever assembly.

The Park/Neutral contacts output to the BCU. The Reverse contacts output to the BCU, the reversing lamps, the Self Leveling & Anti-lock Brakes System Electronic Control Unit (SLABS ECU) and, where applicable, the Active Cornering Enhancement Electronic Control Unit (ACE ECU) and the electrochromatic interior mirror.

Scheme 11

GEAR RATIOS

GEAR RATIOS

GEAR SELECTOR CABLE

The selector cable is a Bowden type cable that connects the gear selector lever assembly to a gear selector lever on the automatic transmission. "C" clips secure the ends of the outer cable to brackets on the gear selector lever assembly and the gear selector lever. The inner cable is adjustable at the connection of the inner cable with the automatic transmission gear selector lever.

GEAR SELECTOR LEVER ASSEMBLY

Note. If the battery becomes discharged, the interlock system will prevent selector lever movement and removal of the ignition key.

The selector lever assembly consists of a lever and a cover attached to a base. (Scheme 12) The base is located on a gasket and secured to the transmission tunnel. The lever is hinged to the base. A latch in the lever engages with detents in the base to provide the lever positions P, R, N, D, 3, 2, 1. The latch is disengaged by pressing a release button on the lever knob. Except for lever movement between positions D and 3, the button must be pressed before the lever can be moved. Some vehicles incorporate an interlock solenoid at the bottom of the lever, which prevents the lever being moved from P unless the ignition switch is on and the foot brake is applied.

The cover incorporates lever position indicators and mode switch. The lever position indicators illuminate to show the position of the selector lever. Illumination is controlled by the Body Control Unit (BCU). The mode switch is a non-latching hinged switch that, when pressed, connects ground to the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) to request a change of mode.

An electrical connector at the rear of the cover connects the selector lever assembly to the vehicle wiring.

Scheme 12

LOCK-UP SOLENOID VALVE (MV3) & SHIFT CONTROL SOLENOID VALVES (MV1 & MV2)

Lock-up solenoid valve (MV3) and shift control solenoid valves (MV1 & MV2) are located on the valve body. (Scheme 3) The purpose of shift control solenoid valves MV1 and MV2 is to switch the hydraulic valves and thus control the hydraulic logic for gear selection. Lock-up solenoid valve MV3 is used to lock the torque converter. The solenoid valves are activated when output control circuits pins are grounded. When transmission is in 1st gear, shift control solenoid valve MV1 is not energized, and shift control solenoid valve MV2 is energized. When transmission is in 2nd gear, shift control solenoid valve MV1 is energized, and shift control solenoid valve MV2 is energized. When transmission is in 3rd gear, shift control solenoid valve MV1 is energized, and shift control solenoid valve MV2 is not energized. When transmission is in 4th gear, neither shift control solenoid valves are energized.

LOCK-UP SOLENOID VALVE (MV3) & SHIFT CONTROL SOLENOID VALVES (MV1 & MV2) CIRCUIT SPECIFICATIONS

PRESSURE REGULATOR SOLENOID VALVE

Pressure regulator solenoid valve is located on the valve body. (Scheme 3) The purpose of the pressure regulator solenoid valve is to generate modulation pressure for the automatic transmission clutches. It is driven by a pulse width modulated power signal that is generated and regulated in the Electronic Automatic Transmission Electronic Control Unit (EAT ECU). The pulse width modulated signal frequency is generated permanently. The free running duty cycle corresponds to the minimal current and the maximal modulation pressure.

PRESSURE REGULATOR CIRCUIT SPECIFICATIONS

TRANSMISSION FLUID COOLER

Transmission fluid from the automatic transmission is circulated through a transmission fluid cooler attached to the front of the radiator. (Scheme 13) Quick release connectors on the transmission fluid lines attach to connections on each end tank of the transmission fluid cooler. A transmission fluid temperature sensor on the right end tank provides the instrument cluster with an input of transmission fluid temperature. If the temperature exceeds a preset limit, the instrument cluster illuminates the transmission temperature warning lamp. (Scheme 14) The warning lamp remains illuminated until the temperature of the transmission fluid returns within limits.

Scheme 13

Scheme 14

When the ignition is switched on, a bulb check is performed on the transmission temperature warning lamp and the mode warning lamps by the instrument cluster and the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) respectively. The warning lamps are illuminated for approximately 3 seconds and then extinguished. (Scheme 14)

The gear position switch outputs are monitored by the Body Control Unit (BCU) and the EAT ECU. The BCU outputs gear position signals to illuminate the position indicators each side of the gear selector lever and on the odometer Liquid Crystal Display (LCD) in the instrument cluster.

In D, 3, 2, and 1, the EAT ECU outputs control signals to the automatic transmission to select the required gear.

In D, all forward gears are available for selection by the EAT ECU. In 3, 2 and 1, a corresponding limit is imposed on the highest gear available for selection. When R is selected, reverse gear only engages if the vehicle is stationary or moving at 5 MPH (8 km/h) or less. When R is deselected, reverse gear only disengages if the vehicle is moving at 4 MPH (6 km/h) or less.

DIAGNOSTICS

If there is a fault, the automatic transmission will attempt to drive as normally as possible. However, if it is not safe to continue changing gears, a limp home mode will be selected.

Limp home mode differs depending upon the vehicle conditions when the fault is diagnosed. If high range is selected, the transmission will default to 3rd gear (if vehicle is stationary) and 4th gear (if vehicle moving). If low range is selected, then the system will attempt to maintain the current gear until the ignition supply is removed. This is in case the fault occurs while negotiating a steep gradient.

If there is a fault which either prevents all gears being used or disables the kick-down facility, the sport and manual lights will flash at the same time. This indicates to the driver that the vehicle has entered limp home mode. This mode will continue until the ignition is turned off. When the ignition is turned back on and the engine has been cranked, the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) will complete a self-test. If the fault has rectified itself the automatic transmission will resume normal operation and the sport and manual lights will no longer flash. If a fault has been rectified or is no longer present but the fault code has not been deleted, the sport and manual lights will continue to flash until the EAT ECU has diagnosed the fault is no longer present.

If any of the above conditions are true, the software within the transmission EAT ECU will have stored a fault code. After a fault code has been stored and the vehicle has completed 40 warm-up cycles, the vehicle fault code will be deleted from memory providing the fault does not reappear during this time. A warm-up cycle is completed when a running engines coolant temperature rising by at least 61 F° (16 C°) and exceeding 158 F° (70 C°). If the fault codes reappear, this counter is reset and requires another 40 warm-ups before the fault is deleted automatically.

If the automatic transmission EAT ECU is found to have been disconnected, the vehicle will have selected an hydraulic limp home mode. Reconnection must occur when the ignition is switched off. If the EAT ECU was disconnected while the ignition was turned on, fault codes will have been stored within the ECM and EAT ECU. These fault codes must be deleted using Land Rover TestBook/T4 scan tool or other suitable scan tools.

While the ignition is on, the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) diagnoses the system for faults. The extent of the diagnostic capability at any particular time depends on the prevailing operating conditions (e.g. it is not possible to check torque converter lock-up while the vehicle is stationary, or to check for a short circuit to ground if the circuit concerned is already at a low potential).

If a fault is detected, the EAT ECU immediately stores a fault code and the values of 3 operating parameters associated with the fault. Depending on the fault, there are 4 possible effects

1. The fault has little effect on automatic transmission operation or vehicle emissions. The driver will probably not notice any change and the warning lamps remain extinguished.
2. The fault has little effect on automatic transmission operation but may effect vehicle emissions (e.g. torque converter not functioning or 3rd/ 4th gear permanently selected) and if the fault is detected on a second consecutive drive cycle, the MIL illuminates.
3. All gears are available but kickdown does not function. The sport and manual warning lamps flash. The MIL remains extinguished.
4. Limp home mode is selected and vehicle performance is greatly reduced. The sport and manual warning lamps flash and if the fault is detected on a second consecutive drive cycle, the MIL illuminates.

After the detection of a fault, the effects remain active for the remainder of the drive cycle. In subsequent drive cycles, as soon as the EAT ECU diagnoses the fault is no longer present, it resumes normal control of the automatic transmission. The conditions required to diagnose that the fault is no longer present depend on the fault. Some faults require the engine to be started, others require only that the ignition is switched on.

Only 5 different faults can be stored in the memory at any one time. If a further fault occurs, the fault with the lowest priority will be replaced by the new fault.

Controller Area Network

The Controller Area Network (CAN) is a high speed serial interface for transmitting information between control modules. CAN communications are "self checked" for errors and if an error is detected, the message is ignored by the receiving control module. Due to the high rate of information exchange, the system has a high degree of latency (at rest time, waiting for information to process). This allows for an error to be present without reducing the overall data transfer rate.

On Board Diagnostic System

The Electronic Automatic Transmission Electronic Control Unit (EAT ECU) communicates with the Engine Control Module (ECM) via a CAN interface. This is used by the transmission for the gearshift torque interface and as a means for transmitting On Board Diagnostic (OBD) information between the EAT ECU and ECM. The EAT ECU requests the ECM that freeze frame data is stored, and requests MIL activation. If the MIL is illuminated without any fault codes being stored in the ECM, then the EAT ECU is requesting MIL activation. The EAT ECU MIL activation request can be checked with Land Rover Textbook/T4 scan tool.

COMPENSATION FOR REDUCED ENGINE TORQUE

In a similar way to the Towing mode, if the vehicle is producing less torque than would normally be the case (high altitude or very hot ambient air), the transmission will hold onto gears longer than would normally be the case. This is a very similar situation to towing, but the performance of the vehicle is reduced due to a lack of engine power, rather than the weight of the vehicle.

GEAR SELECTOR LEVER INTERLOCK

The interlock solenoid on the selector lever is de-energized unless the foot brake is applied while the ignition is on. While de-energized, the interlock solenoid allows the selector lever to move through the range unless P is selected. On entering the P position, the interlock solenoid engages a latch which locks the selector lever. When the ignition is on and the foot brake is applied, the Body Control Unit (BCU) energizes the interlock solenoid, which disengages the latch and allows the selector lever to be moved out of P.

HIGH/LOW RANGE

The high range gears should be used for all normal driving, including off-road driving across dry level terrain. If the gear lever is moved from drive to a lower gear while the vehicle is moving at speed, the selected gear will be engaged only when the road speed is reduced to an acceptable level. This prevents the possibility of the engine from over-revving.

Low range gears should be selected in any situation where low speed maneuvering is necessary, extreme off-road condition driving is required or Hill Descent Control (HDC) is required. Selection is made via the HI/LO lever situated on the vehicle's center console.

KICKDOWN

The Electronic Automatic Transmission Electronic Control Unit (EAT ECU) monitors the input of the throttle position sensor to determine when kickdown is required. When it detects a kickdown situation, the EAT ECU immediately initiates a down shift provided the target gear will not cause the engine speed limit to be exceeded.

MODE SELECT

In addition to providing drive, and electronically controlling the gear changes throughout the conventional gear selection range in both high and low ranges, the automatic transmission system also incorporates a mode select facility. This feature enables the driver to select the gear change strategy that most suits the current driving conditions. The mode switch, situated adjacent to the rear of the automatic selector gate, can be used to select a Sport mode when in high range, and Manual mode when low range is selected. During the power-up procedure after the ignition is switched on, the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) defaults to an economy mode.

Sport Mode

Sport mode can be selected by pressing the mode button whenever high range is engaged. Once sport mode has been selected, an instrument cluster lamp will illuminate the letter "S". (Scheme 14) Although automatic gear shifts continue to be controlled by the Electronic Automatic Transmission Electronic Control Unit (EAT ECU), they will be made using a different strategy (i.e. remaining in a given gear longer when accelerating, and changing down to a lower gear earlier when decelerating). The characteristics of the transmission while in sport mode help make optimum use of the engine's power. Pressing the mode button for a second time returns the transmission system to its normal operation within the high range.

Manual Mode

Manual mode is selected by pressing the mode button whenever low range is selected. With manual mode selected an instrument cluster will illuminate the letter "M". (Scheme 14) The transmission will function in a similar way to a manual transmission. In this condition the transmission will change into the selected gear as soon as possible, and then remain in that gear at all speeds, changing down only to prevent engine stall. For example, if the selector position is in "3" while driving in normal modes, gears 1, 2 and 3 will be available However, in manual mode, if position "3" is selected, the transmission will select 3rd gear very shortly after pulling away from rest. This mode is designed to give improved off road performance. Kickdown is disabled in this mode. Downshifts occur only to prevent the engine stalling. From a standing start, the vehicle pulls away in 1st gear and, if a higher gear is selected, upshifts almost immediately to the selected gear (shifts of more than one gear can occur).

SHIFT CONTROL

To provide the different driving characteristics for each mode of operation, the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) incorporates different shift maps of throttle position/engine speed. Base shift points are derived from the appropriate shift map. When a shift is required, the EAT ECU sends a request to the Engine Control Module (ECM) for a reduction in engine torque (by reducing ignition timing), in order to produce a smoother shift. The percentage of torque reduction requested varies according to the operating conditions at the time of the request. When the EAT ECU receives confirmation of the torque reduction from the ECM, it then signals the shift solenoid valves in the automatic transmission to produce the shift. To further improve shift quality, the EAT ECU also signals the pressure regulating solenoid valve to modulate the hydraulic pressure and so control the rate of engagement and disengagement of the brake clutches.

With time, the components in a automatic transmission wear and the duration of the gear shifts tends to increase, which has an adverse effect on the brake clutches. To counteract this, the EAT ECU applies a pressure adaptation to each shift. To calculate the adaptations, the EAT ECU monitors the pressure modulation used, and time taken, for each shift. If a subsequent shift of the same type, in terms of throttle position and engine speed, has a longer duration, the EAT ECU stores an adaptation for that type of shift in a volatile memory. The adaptation is then included in future pressure calculations for that type of shift, to restore shift duration to the nominal.

TORQUE CONVERTER LOCK-UP

Incorporated into the design of the automatic transmission system is a lock-up torque converter feature, where the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) will activate the torque converter lock-up solenoid. When activated, the torque converter lock-up clutch will be engaged and no slip will be allowed. Direct drive through the torque converter will be provided in this condition.

The torque converter can be locked and unlocked during driving to improve driveability, fuel consumption and gear changing. The torque converter will not be locked until the transmission has calculated that the oil temperature has reached a predetermined temperature. This is calculated from the engine coolant temperature via a software timer within the EAT ECU. The length of this timer depends on several variables, including the engine coolant temperature during cranking, but is approximately as follows. With engine coolant temperature at about 77 F° (25 C°) the transmission does not take any time to warm up. With engine coolant temperature at 32 F° (0 C°) it takes the transmission fluid 7 minutes to warm up. With engine coolant temperature at about -13 F° (-25 C°) it takes the transmission fluid 12 minutes to warm up.

To enhance off road control, particularly when maneuvering at low speeds, torque converter lock-up does not occur when there is any degree of throttle opening. But when the throttle is closed above a preset engine speed, the lock-up clutch engages to provide maximum engine braking by locking the torque converter in any gear at zero percent throttle. This improves engine braking while negotiating steep gradients. This feature will be active only while there is no danger of stalling the engine.

TOWING/STEEP GRADIENTS

Towing/steep gradients When the vehicle is in normal mode (i.e. high range with sport not selected) the automatic transmission will select a shift pattern appropriate to the current conditions. If a heavy load is being pulled, a steep gradient is being climbed or both, the automatic transmission will use a more aggressive shift pattern, compensating for the load by using higher engine speeds for any given throttle angle.

COMPONENT LOCATIONS

COMPONENT LOCATIONS

Scheme 15

TROUBLE SHOOTING

Note. Any diagnosis should begin with confirming the customer's complaint. If possible, road test vehicle first, and note transmission performance for future reference during diagnosis.

PRELIMINARY INSPECTION

1. Transmission malfunctions could be caused by poor engine performance, improper adjustments or failure of hydraulic, mechanical or electronic components. Prior to diagnosing transmission concerns, always begin by checking transmission fluid level, transmission fluid condition and shift cable adjustment. See appropriate AUTOMATIC TRANSMISSION SERVICING article.
2. Check transmission fluid level and condition. Check transmission fluid color. DEXTRON ATF is darker than other types of transmission fluid. To analyze transmission fluid condition see «TRANSMISSION FLUID ANALYSIS»(/land-rover/discovery/l318-2002-2004/remont/automatic-trans/#automatic-transmission-diagnosis-with-codes) table. Normally torque converter is not drained or serviced. Regular transmission fluid changes keep additive strength high enough to cope with several quarts of used transmission fluid in the transmission when it is serviced. The only practical method of cleaning the torque converter is through specialized flushing equipment.
3. Ensure engine starts with gearshift lever in Park and Neutral to ensure proper adjustment of park/neutral position switch. See appropriate AUTOMATIC TRANSMISSION SERVICING article.
4. Ensure all system-related fuses are okay. Check wire harnesses for proper routing. Verify all harness and component connections are clean and tight. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-2002-2004/remont/automatic-trans/#automatic-transmission-diagnosis-with-codes) . If area of fault cannot be located or repaired during preliminary inspection, check self-diagnostic system. See appropriate SELF-DIAGNOSTIC SYSTEM article in ENGINE PERFORMANCE. Repair as necessary.
5. Perform road test to determine if problem has been corrected. See «TORQUE CONVERTER ROAD TEST»(/land-rover/discovery/l318-2002-2004/remont/automatic-trans/#automatic-transmission-diagnosis-with-codes__torque-converter-road-test) under PERFORMANCE TESTS.

TRANSMISSION FLUID ANALYSIS

SYMPTOM DIAGNOSIS

Note. Perform PRELIMINARY INSPECTION prior to diagnosing by symptom.

Note. Use the following symptoms to aid in preliminary diagnosis. If a listed symptom matches the customer's concern, check the applicable items for possible cause.

Abrupt Or Jerky Gear Changes

Abrupt or jerky gear changes could be caused by pressure regulator solenoid valve screen mesh being blocked. To correct the problem, pressure regulator solenoid valve must be replaced with a new one that has a larger screen mesh. See Land Rover TSB 44/01/03/NAS dated September 12, 2003 SHIFT QUALITY IMPROVEMENT .

Harsh Gear Changes, Poor Gear Selection, Gear Slip Or Loss Of Drive Or Intermittent Failure Of Park Lock Function

Harsh gear changes, poor gear selection, gear slip or loss of drive and intermittent failure of park lock function could be caused by water contamination of transmission fluid. The contamination of the transmission fluid could have been caused by an improperly positioned automatic transmission breather tube. Condensation from air conditioning and water from deep wading can flow over the transmission and collect on an improperly positioned automatic transmission breather tube. The water can then migrate up the transmission tube. Over time these small water droplets can cause an accumulation of water in the transmission. To correct the problem the breather tube must be repositioned. See Land Rover TSB D233 dated December 8, 2000 AT BREATHER REPOSITIONING AND FLUID CHECK .

Large Amount Of Friction Material In Pan Or On Filter Screen

A large amount of friction material in the pan or on the filter screen may indicate that transmission needs to be replaced. Simply servicing the transmission invites future problems as fresh additives can brake loose varnish and other residue and cause problems in the valve body.

Loss Of Drive Or Slipping Transmission

To troubleshoot loss of drive or slipping transmission, see Land Rover TSB 4/01/02/NAS dated August 16, 2002 ZF TRANSMISSION TROUBLESHOOTING .

Transmission Fluid Leaking Out Of Dipstick Tube

Transmission fluid "Mysteriously" expelling from dipstick tube especially after a long drive or when towing could be caused by an overfilled transmission. It could also be caused by water getting into and freezing in the automatic transmission breather tube. To correct water getting into and freezing in automatic transmission breather tube the breather tube must be modified. See Land Rover TSB D352 dated January 12, 1999 TRANSMISSION BREATHER TUBE .

Transmission Shifting Erratically

Transmission shifting erratically could be caused by overfilling or underfilling transmission fluid. With transmission overfilled, transmission fluid will foam and air will enter valve body and clutch circuits. With transmission underfilled, transmission fluid will also foam and pump cavitation will normally result.

Transmission Slipping On Acceleration, Erratic Upshifts, Vehicle Jerking While Accelerating Or Engine Revs (Flares) On Upshift

To troubleshoot transmission slipping on acceleration, erratic upshifts, vehicle jerking while accelerating and engine revving (flaring) on upshift see Land Rover TSB 4/01/02/NAS dated August 16, 2002 ZF TRANSMISSION TROUBLESHOOTING .

TORQUE CONVERTER ROAD TEST

Note. A torque converter with a seized stator will be indicated by vehicle exhibiting good off line performance but sluggishness at higher speeds and excessive fuel consumption.

1. Torque converter lockup can occur in either 3rd or 4th gear at speeds between 30-45 MPH (48-72 kph) and is dependent on load. A quick check of lockup can be made while driving at a steady speed in either 3rd or 4th gear.
2. Slowly accelerate vehicle to speed greater than 30 MPH (48 kph). Press down accelerator briefly and observe tachometer. If tachometer moves 300-500 RPM but speed remains constant Direct Drive Clutch (DDC) did not engage and torque converter did not lockup. If tachometer does not move, DDC engages and torque converter locks up.

HYDRAULIC PRESSURE TESTS

Pressure gauge can be connected to read either mainline or torque converter pressure depending on which test port is selected. Testing can be done on the road, in the shop or both. Install NEW sealing washer when done.

1. Use a 6-mm Allen socket to remove plug. Connect pressure gauge adaptor to appropriate test port. (Scheme 16) For mainline pressure, go to next step. For torque converter pressure, go to step 3.
2. Mainline pressures should be 145-155 psi (1020-1090 kPa) in Drive, 3rd, 2nd and 1st gear at 2000 RPM (under load). Pressure should be zero psi in Park, Neutral and Reverse at all engine speeds. Full mainline pressure will only be seen at "stall" or on a full throttle road test. The Electronic Automatic Transmission Electronic Control Unit (EAT ECU) reduces mainline pressure during light throttle applications. Lower than normal mainline pressure can indicate a worn pump, leaking clutch or clutch brake pistons, or more typically a partially clogged filter screen or low transmission fluid level.
3. Torque converter pressure should be 95-105 psi (665-735 kPa) in all gears, Park and Neutral at 2000 RPM. Pressure should be zero psi with Direct Drive Clutch (DDC) engaged.

Scheme 16

STALL SPEED TEST

Note. Specifications provided were measured at sea level with an ambient temperature of 68 F° (20 C°). At higher altitudes or higher ambient temperatures, these figures will be reduced.

Note. A torque converter with a seized stator will not show up on a stall test. See TORQUE CONVERTER ROAD TEST for additional information.

The "Stall" in stall testing occurs when turbine portion of the torque converter is prevented from turning (stalled) by vehicle brakes with vehicle in gear at Wide Open Throttle (WOT). A stall test will reveal the following

1. Slipping clutches, clutch brakes and unidirectionals (one way clutches).
2. A freewheeling torque converter stator.
3. Weak or poorly tuned engine.

Since stall testing is done with brakes fully locked and zero road speed, it will be possible to test holding/driving power of components responsible for 1st gear in Drive, 3rd, 2nd, 1st and Reverse gear. A stall test will not reveal problems with clutches or clutch brakes specifically responsible for 2nd, 3rd or 4th gear, but by testing 1st and Reverse the following components can be confirmed or eliminated as being a problem

1. "A" clutch that is used in all forward gears.
2. "C" clutch that is used in 1st, 2nd, 3rd and Reverse gears.
3. Clutch brake No. 3 (CB3) that is used in 1st (gear selector lever position 1) gear.
4. Unidirectional No. 2 (UD2) that is used for holding Drive, 3rd and 2nd gear positions.

1. Ensure powertrain is at normal operating temperature and that transmission, coolant and engine oil are topped off. Connect Land Rover Textbook/T4 scan tool or an accurate tachometer to vehicle. The vehicle tachometer is NOT acceptable for stall testing. Block wheels and apply both hand brake and foot brake firmly. Start engine and place gear selector lever in "D".
2. Depress accelerator to floor and hold until engine speed stabilizes. Release accelerator and record the stall engine speed. DO NOT hold the throttle at Wide Open Throttle (WOT) for more than 10 seconds. Stall engine speed should be 2200-2400 RPM. See «STALL TEST RESULT»(/land-rover/discovery/l318-2002-2004/remont/automatic-trans/#automatic-transmission-diagnosis-with-codes) table. Shift to Neutral and hold engine speed at idle 30 minutes to cool the transmission fluid. Repeat in 1st gear selector lever position and record the stall engine speed. Shift to Neutral and hold engine speed at idle 30 minutes to cool the transmission fluid. Repeat in Reverse gear and record the stall engine speed.

STALL TEST RESULT

CLUTCH & SERVO AIR CHECKS

Note. For additional information, refer to overhaul procedures. See appropriate OVERHAUL article.

TEST PROCEDURE

The Electronic Automatic Transmission Electronic Control Unit (EAT ECU) is able to store freeze frame data-like information. It stores 3 parameters (variables) during the first occurrence of a fault code. These parameters are not refreshed if the fault code reoccurs. Land Rover Textbook/T4 scan tool is able to retrieve these variables. After retrieving the stored variables, they must be multiplied by appropriate conversion factors in order to obtain the freeze frame data value. (Scheme 17) Each fault code will have a set of 3 variables assigned to it. Use the conversion table to obtain the proper freeze frame data value. (Scheme 17)

When a fault code diagnostic test indicates that the EAT ECU is faulty or other transmission electrical device is faulty, check the entire electrical circuit associated with that device before replacing it. See WIRING DIAGRAMS . When diagnosing a transmission problem, suspect electrical failure before suspecting mechanical failure.

Scheme 17

POWER OR COMMUNICATION LOST TO ELECTRONIC AUTOMATIC TRANSMISSION ELECTRONIC CONTROL UNIT

If the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) is connected, but the Land Rover Textbook/T4 scan tool cannot communicate with it, then the power supply to the EAT ECU may have been lost or the diagnostic line is not connected. In this instance, the following sequence of events should be followed

1. Turn the ignition to the OFF position.
2. Disconnect the EAT ECU.
3. Test the voltage at EAT ECU harness connector terminal No. 26 (permanent power supply) with a volt meter. This should read greater than 10 volts.
4. Measure the resistance between ground and EAT ECU harness connector terminal No. 6 (power ground) and terminal No. 28 (electronics ground) using a digital ohmmeter or equivalent. The resistance should be less than 10 ohms.
5. Turn ignition on.
6. Test the voltage at EAT ECU harness connector terminal No. 54 (ignition power supply) with a volt meter. This should read greater than 10 volts.
7. If the above is completed with no strange reading, the EAT ECUs power supply is okay. The only possibility is the diagnostic connector is not attached to the EAT ECU. To check for this, measure the resistance between terminal No. 31 of the EAT ECU connector, and terminal No. 7 of the vehicle diagnostic connector. This should be less than 10 ohms.

RETRIEVING DIAGNOSTIC TROUBLE CODES

The first digit of the Diagnostic Trouble Code (DTC) defines whether the DTC set is a Federally mandated DTC (P0XXX) or a Land Rover DTC (P1XXX). A Land Rover Textbook/T4 scan tool can retrieve and diagnose all DTCs. An OBD-II compliant scan tool can only retrieve and diagnose Federally mandated DTCs. Refer to scan tool manufacturer's user manual for specific procedures. For DTCs, see DIAGNOSTIC TROUBLE CODE DEFINITIONS table.

SYSTEM MONITORS

Note. The following monitors describe criteria, monitoring structure, parameters and values used by and programmed into the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) to determine a system failure, store fault codes and illuminate the Malfunction Indicator Light (MIL).

End Of Line Programming Monitoring

For end of line programming monitoring information (Scheme 18)

Note. This monitor covers information for DTC P1602.

Scheme 18

Gear Ratio Functional Check Monitoring

For gear ratio functional check monitoring information (Scheme 19)

Note. This monitor covers information for DTC P0721 and P0731-P0734.

Scheme 19

Pressure Regulator Solenoid Monitoring

For pressure regulator solenoid monitoring information (Scheme 20)

Note. This monitor covers information for DTC P0748.

Scheme 20

Shift Solenoids Monitoring

For shift solenoids monitoring information (Scheme 21)

Note. This monitor covers information for DTC P0753 & P0758.

Scheme 21

System Interface Monitoring

For system interface monitoring information (Scheme 22)and (Scheme 23).

Note. This monitor covers information for DTC P1705, P1841-P1843 and P1884.

Scheme 22

Scheme 23

Torque Converter Clutch Solenoid Monitoring

For torque converter clutch solenoid monitoring information (Scheme 24)

Note. This monitor covers information for DTC P0722, P0741 and P0743.

Scheme 24

Transmission Control Module Monitoring

For Transmission Control Module (TCM) monitoring information (Scheme 25)

Note. This monitor covers information for DTC P1562, P1601, P1606, P1612 and P1613.

Scheme 25

DIAGNOSTIC TROUBLE CODE DEFINITIONS

DIAGNOSTIC TROUBLE CODE DEFINITIONS

CLEARING DIAGNOSTIC TROUBLE CODES

Diagnostic Trouble Codes (DTCs) can be cleared using a Land Rover Textbook/T4 scan tool or OBD-II compliant scan tool. Follow Textbook/T4 system or scan tool manufacturer instructions. After a fault has not recurred for 40 warm-up cycles, the fault is deleted from the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) memory.

SUMMARY

If no hard DTCs are present, and driveability symptoms or intermittent DTCs exist, attempt diagnosis by symptom, or by testing individual components related to system fault. See TROUBLE SHOOTING .

Note. Always clear DTCs once repairs are complete. See CLEARING DIAGNOSTIC TROUBLE CODES . Road test vehicle and retrieve DTCs to determine if complaint or DTC is repaired.

FAULT CODE 01: TRANSMISSION RELAY CONTROL (RELAY STICKS, SHORT CIRCUIT)/SOLENOID VALVES POWER SUPPLY RELAY STICKING OPEN OR SHORT CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 26)- (Scheme 28). Freeze frame variables are AN6, AN7 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 26

Scheme 27

Scheme 28

FAULT CODE 02: TRANSMISSION RELAY CONTROL (RELAY STICKS, OPEN CIRCUIT)/SOLENOID VALVES POWER SUPPLY RELAY STICKING CLOSED OR OPEN CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 29)- (Scheme 31). Freeze frame variables are AN6, AN7 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 29

Scheme 30

Scheme 31

FAULT CODE 03: EEPROM COMMUNICATION FAULT/ECU FAULT, EEPROM COMMUNICATION

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 32)and (Scheme 33). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 32

Scheme 33

FAULT CODE 04: EEPROM CHECKSUM FAULT/ECU EEPROM CHECKSUM

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 34)and (Scheme 35). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 34

Scheme 35

FAULT CODE 05: TORQUE CONVERTER LOCK-UP CLUTCH MONITORING/TORQUE CONVERTER LOCK-UP CLUTCH FAULT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code may affect driveability.

For fault code description and diagnostic test procedure (Scheme 36)- (Scheme 38). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 36

Scheme 37

Scheme 38

FAULT CODE 06: WATCHDOG CHECK, ECU FAULT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 39)and (Scheme 40). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 39

Scheme 40

FAULT CODE 08: SOLENOID VALVE 1 CHECK (SHORT CIRCUIT TO VOLTAGE)/SHIFT SOLENOID (MV1) SHORT CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 41)and (Scheme 42). Freeze frame variables are N-MOT, AN6 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 41

Scheme 42

FAULT CODE 09: SOLENOID VALVE 2 CHECK (SHORT CIRCUIT TO VOLTAGE)/SHIFT SOLENOID (MV2) SHORT CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 43)and (Scheme 44). Freeze frame variables are N-MOT, AN7 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 43

Scheme 44

FAULT CODE 10: PRESSURE REGULATOR CHECK (SHORT CIRCUIT TO VOLTAGE)/PRESSURE REGULATING SOLENOID (MV4) SHORT CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 45)and (Scheme 46). Freeze frame variables are N-MOT, VGT-$X and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 45

Scheme 46

FAULT CODE 11: CAN MESSAGE MD-REIB INVALID (FFH)/CAN MESSAGE: ENGINE FRICTION INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 47)and (Scheme 48). No diagnostic test procedure available from manufacturer. Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 47

Scheme 48

FAULT CODE 12: MES LINE 1 FAULT/BECM TO MESSAGE CENTER CIRCUIT FAULT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will be set when SPORT/MANUAL lamp fails bulb check or when SPORT/MANUAL lamp is permanently illuminated. It will also have no effect on transmission operation.

For fault code description and diagnostic test procedure (Scheme 49)and (Scheme 50). Freeze frame variables are N-MOT, AN9 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 49

Scheme 50

FAULT CODE 13: MES LINE 2 FAULT/BECM TO MESSAGE CENTER CIRCUIT FAULT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will be set when SPORT/MANUAL lamp fails bulb check or when SPORT/MANUAL lamp is permanently illuminated. It will also have no effect on transmission operation.

For fault code description and diagnostic test procedure (Scheme 51)and (Scheme 52). Freeze frame variables are N-MOT, AN11 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 51

Scheme 52

FAULT CODE 14: GEAR POSITION SWITCH MONITORING (PERMANENT)/GEAR POSITION SWITCH INCORRECT OUTPUTS

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range, limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 53)- (Scheme 60). Freeze frame variables are N-MOT, YPO-Old and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 53

Scheme 54

Scheme 55

Scheme 56

Scheme 57

Scheme 58

Scheme 59

Scheme 60

FAULT CODE 15: CAN LEVEL MONITORING

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range and limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 61)and (Scheme 62). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 61

Scheme 62

FAULT CODE 16: CAN BUS MONITORING/CAN BUS FAULT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range, limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 63)- (Scheme 65). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 63

Scheme 64

Scheme 65

FAULT CODE 17: CAN TIME-OUT MONITORING

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range and limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 66)- (Scheme 68). Freeze frame variables are N-MOT, VGT-$X and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 66

Scheme 67

Scheme 68

FAULT CODE 18: CAN MESSAGE WFPDK (THROTTLE ANGLE) IN INVALID (FFH)/CAN MESSAGE: THROTTLE POSITION INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause a substitute throttle angle of 50 percent to be adopted. It will also cause no kickdown and transmission will operate in economy mode only.

For fault code description and diagnostic test procedure (Scheme 69)and (Scheme 70). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 69

Scheme 70

FAULT CODE 19: CAN MESSAGE T-MOT INVALID (FFH)/CAN MESSAGE: ENGINE TEMPERATURE INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause a substitution of engine temperature that will be derived from other inputs. The fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 71)and (Scheme 72). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 71

Scheme 72

FAULT CODE 20: CAN MESSAGE V3 (ROAD SPEED) INVALID (FFH)/CAN MESSAGE: ROAD SPEED INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 73)and (Scheme 74). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 73

Scheme 74

FAULT CODE 21: DOWNSHIFT SAFETY MONITORING/DOWNSHIFT SAFETY MONITOR PREVENTED DOWNSHIFT WHICH WOULD HAVE CAUSED ENGINE OVERSPEED

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range, limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 75)- (Scheme 77). Depending on conditions, fault code 21 may be caused by the same failures that cause fault code 22. Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 75

Scheme 76

Scheme 77

FAULT CODE 22: STALL SPEED MONITORING/TORQUE CONVERTER SLIPPING

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range, limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 78)- (Scheme 80). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 78

Scheme 79

Scheme 80

FAULT CODE 23: GEAR POSITION SWITCH DURING CRANKING/GEAR POSITION SWITCH INCORRECT OUTPUTS

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range and limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 81)and (Scheme 82). Freeze frame variables are N-MOT, YPO-Old and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 81

Scheme 82

FAULT CODE 24: BATTERY SUPPLY CHECK/BATTERY SUPPLY BELOW 9 VOLTS WHILE ENGINE IS RUNNING

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range, limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 83)and (Scheme 84). Freeze frame variables are N-MOT, MMM and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 83

Scheme 84

FAULT CODE 25: SOLENOID VALVE FOR TC (SHORT CIRCUIT TO GROUND, OR OPEN CIRCUIT)/TORQUE CONVERTER LOCK-UP SOLENOID (MV3) OPEN CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 85)and (Scheme 86). Carry out test as for fault code 28 but substitute terminal No. 32 in place of terminal No. 5. Freeze frame variables are N-MOT, AN8 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 85

Scheme 86

FAULT CODE 26: SOLENOID VALVE 1 (LINE SHORT CIRCUIT GROUND, OR OPEN CIRCUIT)/SHIFT SOLENOID (MV1) OPEN CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 87)and (Scheme 88). Carry out test as for fault code 30 but substitute terminal No. 32 in place of terminal No. 5. Freeze frame variables are N-MOT, AN6 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 87

Scheme 88

FAULT CODE 27: SOLENOID VALVE 2 (LINE SHORT CIRCUIT GROUND, OR OPEN CIRCUIT)/SHIFT SOLENOID (MV2) OPEN CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 89)and (Scheme 90). Carry out test as for fault code 33 but substitute terminal No. 32 in place of terminal No. 5. Freeze frame variables are N-MOT, AN7 and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 89

Scheme 90

FAULT CODE 28: PRESSURE REGULATOR (LINE SHORT CIRCUIT TO GROUND, OR OPEN CIRCUIT)/PRESSURE REGULATING SOLENOID (MV4) OPEN CIRCUIT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause the transmission to switch to limp home mode in low and high ranges. It will also cause a shift in pressure to maximum, and harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 91)and (Scheme 92). Freeze frame variables are N-MOT, VGT-$X and UBATT. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 91

Scheme 92

FAULT CODE 29: GEAR RATIO MONITORING, 1ST GEAR/RATIO MONITORING IMPLAUSIBLE 1ST GEAR RATIO

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 93)- (Scheme 96). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 93

Scheme 94

Scheme 95

Scheme 96

FAULT CODE 30: GEAR RATIO MONITORING, 2ND GEAR/RATIO MONITORING IMPLAUSIBLE 2ND GEAR RATIO

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 97)- (Scheme 100). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 97

Scheme 98

Scheme 99

Scheme 100

FAULT CODE 31: GEAR RATIO MONITORING, 3RD GEAR/RATIO MONITORING IMPLAUSIBLE 3RD GEAR RATIO

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 101)- (Scheme 104). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 101

Scheme 102

Scheme 103

Scheme 104

FAULT CODE 32: GEAR RATIO MONITORING, 4TH GEAR/RATIO MONITORING IMPLAUSIBLE 4TH GEAR RATIO

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 105)- (Scheme 108). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 105

Scheme 106

Scheme 107

Scheme 108

FAULT CODE 33: CAN MESSAGE MD-IND INVALID, INDICATED BY F-TL-MES/CAN MESSAGE: ENGINE TORQUE INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause a substitution of engine torque that will be derived from other inputs. It may also affect shift quality.

For fault code description and diagnostic test procedure (Scheme 109)and (Scheme 110). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 109

Scheme 110

FAULT CODE 34: CAN MESSAGE MD-IND INVALID (FFH)/CAN MESSAGE: ENGINE TORQUE INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause a substitution of engine torque that will be derived from other inputs. It may also affect shift quality.

For fault code description and diagnostic test procedure (Scheme 111)and (Scheme 112). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 111

Scheme 112

FAULT CODE 35: CAN MESSAGE N-MOT INVALID, INDICATED BY F-N-MOT/CAN MESSAGE: ENGINE SPEED INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will cause transmission to maintain current gear in low range and limp home mode in high range. It will also cause a shift in pressure to maximum, harsh gear shifts and engagement.

For fault code description and diagnostic test procedure (Scheme 113)and (Scheme 114). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 113

Scheme 114

FAULT CODE 37: CAN MESSAGE T-ANS INVALID (FFH)/CAN MESSAGE: ENGINE AIR INTAKE TEMPERATURE INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 115)and (Scheme 116). No diagnostic test procedure is available from manufacturer. Check Engine Management System (EMS) for faults which prevent it from transmitting air inlet temperature. Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 115

Scheme 116

FAULT CODE 38: CAN MESSAGE FHOEHE INVALID (FFH)/CAN MESSAGE: ALTITUDE SHIFT CONTROL INVALID

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will prevent reduced torque compensation. It may cause a reduction in performance/driveability at altitude or high ambient temperatures.

For fault code description and diagnostic test procedure (Scheme 117)and (Scheme 118). No diagnostic test procedure available from manufacturer. Check Engine Management System (EMS) for faults witch prevent it from transmitting air density (altitude calculation). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 117

Scheme 118

FAULT CODE 39: RANGE SWITCH PLAUSIBILITY ERROR/TRANSMISSION HIGH/LOW RANGE IMPLAUSIBLE INPUT

Note. For circuit reference, see WIRING DIAGRAMS .

This fault code will have no apparent effect on the transmission.

For fault code description and diagnostic test procedure (Scheme 119)- (Scheme 121). Freeze frame variables are N-MOT, VGT-$X and MMM. See TEST PROCEDURE under SELF-DIAGNOSTIC SYSTEM.

Scheme 119

Scheme 120

Scheme 121

Scheme 122

Scheme 123

Scheme 124

Transmission Electronic Control System Wiring Diagram (ZF4HP22 - 1999-2000 Discovery). Scheme 125

Transmission Electronic Control System Wiring Diagram (ZF4HP22 - 2001-2002 Discovery). Scheme 126

Transmission Electronic Control System Wiring Diagram (ZF4HP22 & ZF4HP24 - 2003-2004 Discovery). Scheme 127

See also:
• TRANSMISSION FLUID ANALYSIS
• TORQUE CONVERTER ROAD TEST
• 14
• 23
• 21
• 22
• 29
• 30
• 31
• 32
• 05
• 25
• 10
• 28
• 08
• 26
• 09
• 27
• 24
• 04
• 03
• 06
• 02
• 01
• 39
• 12
• 13
• 16
• 15
• 17
• 11
• 18
• 19
• 20
• 33
• 34
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• 38
• TROUBLE SHOOTING
• CLEARING DIAGNOSTIC TROUBLE CODES
• TEST PROCEDURE