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Subject Power steering problems and solutions.
Posted by DVDBURN (MD) on November 07, 2010 at 6:36 AM
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Untitled Document

This write-up is to aid in troubleshooting problems with the power steering system. Electrically and mechanically the PS system in the Z32 is an intricate system which combines multiple sensors and modules to properly function when the vehicle is at rest or traveling at varying speeds.

Here are the most common problems.

1. Hard steering.

2. Very hard steering.

3. Light steering.

4. No steering at all.

5. An intermittent condition of all the above.

Items that are part of the overall PS system.

Electrically Related Parts.

1. ECU.

2. Speed sensor (1990 FSM page EF & EC - 185).

3. Gauge cluster (Referred to as the Combination Meter in the FSM).

4. HICAS Module (twin turbo only) (Symptom chart, 1990 FSM page ST-61), (Self diagnosis, 1990 FSM page ST-68).

5. Power steering control module (NA only, 1990 FSM page ST-38).

6. Steering neutral position switch (1990 FSM page ST-36, page ST-58, page ST-78)

7. Steering angle sensor (1990 FSM page ST-57, page ST-84, page ST-90).

8. HICAS solenoids (twin turbo only) (1990 FSM page ST-86).

9. Fail safe valve solenoid (HICAS only) (Explained in 1990 FSM page ST-31).

10. Power steering solenoid (1990 FSM page ST-37, page ST-88).

11. Power steering oil pressure switch (1990 FSM page EF & EC - 152), (1990 FSM page EF & EC - 190).

12. Power steering fluid level sensor (twin turbo only) (1990 FSM page ST-7).

13. Parking brake switch (1990 FSM page ST-34).

14. Clutch switch (1990 FSM page ST-30) (1990 FSM page ST-34).

15. Stop lamp switch signal (1990 FSM page ST-32).

16. A.S.C.D. (1990 FSM page EL-91).

17. Inhibitor switch (Automatics only) (1990 FSM page ST-30, page AT-82).

Note: In twin turbo models you have a HICAS control module. The power steering control module is part of this module. In NA models you have a power steering control module.

Mechanically related parts.

1. Power steering fluid reservoir/fluid level (NA, 1990 FSM page ST-7) (Twin turbo, 1990 FSM page ST-43)

2. Power steering oil pump (1990 FSM page ST-25).

3. Power steering rack/bleeding (1990 FSM page ST-7) .

4. HICAS steering rack/bleeding (twin turbo only) (1990 FSM page ST-48).

5. Steering wheel shaft lower joint (1990 FSM page ST-11).

Note: The steering wheel shaft lower joint is the swivel joint that connects the steering wheel shaft to the steering rack. I only mention this because in rare cases this joint has been known to wear out causing a hard spot (binding) when trying to turn the steering wheel mistaking the problem to be with the PS system.

Note: Preliminary knowledge helpful in conducting diagnoses can be found in the 1990 FSM on page ST-31.

First, lets look at the mechanical possibilities.

1. Did you use the correct power steering fluid (1990 FSM page ST-7)? The Z32 PS/HICAS system uses ATF Dexron type fluid. It does not use power steering fluid. Using power steering fluid will cause the PS system to break down and eventually render it useless.

2. Correct fluid level (NA, 1990 FSM page ST-7) (Twin turbo, 1990 FSM page ST-43). Here is an excerpt from Nissan technical bulletin NTB90-092. It pertains to 1990-1991 twin turbo Zs but it will most definitely be useful for other years too.

Nissan technical bulletin NTB90-092

APPLIED VEHICLE(S): 1990-91 300ZX Turbo (Z32) Equipped with HICAS System.


On some 1990 & 1991 300ZX Turbo vehicles equipped with the HICAS System, the warning lamp may erroneously illuminate when the engine is cold. This is because the oil level varies based upon the oil temperature.


The method for checking the HICAS oil level has been modified to prevent the erroneous operation of the warning lamp.


• Do not overfill.

• Recommended fluid is Automatic Transmission Fluid "Dexron"

• Note that the fluid level will vary with fluid temperature by approximately 1 mm/5°C (0.04 in/9°F) due to changes in fluid volume.

Checking Fluid Level

1. Check the oil level exactly because it varies with oil temperature.

2. Maintain the fluid level so that the lower surface of the float is maintained between the "L" and "H" marks on the gauge rod, as shown in the illustration below. The fluid level should be checked when the engine is stopped and the fluid temperature is about 30°C (86°F).

3. If the fluid level is below the "L" line, add fluid up to the "H" line.

3. Bleeding the system (1990 FSM page ST-7). It is important that you always bleed the PS system before bleeding the HICAS system. Frequently check and maintain proper PS fluid levels during any bleeding process. Fluid levels (NA, 1990 FSM page ST-7) (Twin turbo, 1990 FSM page ST-43).

Note: It is important that the PS system has been bled. The system needing to be bled can also have an effect on the HICAS system and can cause the HICAS indicator to come on. If the system needs bleeding it can cause intermittent or constant hard steering issues. Here is a simple process to bleed the PS system.

a. Start the engine and let it warm up to operating temperatures (140-176 degrees).

b. Insure you have a proper PS fluid level (using ATF Dexron Type fluid).

c. Place the front of the car on jack stands so that the front tires can clear the floor.

d. REV the engine to 1000-1500 RPMs and hold it there.

e. Turn the steering wheel very fast all the way to the right until it hits the stop limit. Hold it there for no more than 15 seconds. Watch your time on this. You do not want to exceed the amount of time as damage may occur to the PS system.

f. Turn the steering wheel very fast all the way to the left until it hits the stop limit. Hold it there for no more than 15 seconds. Again, watch your time on this. You do not want to exceed the amount of time as damage may occur to the PS system.

g. Repeat steps e and f at least ten more times to insure a good system bleeding.

Symptoms of incomplete air bleeding.

1. Bubbles in the PS reservoir.

2. A clicking noise in the PS pump.

3. A buzzing noise in the PS pump.

Note: Since most of the common problems we experience with the PS system are caused by something other than the bleeding of the HICAS system I am only going to recommend that you use a FSM for how to bleed the HICAS system (1990 FSM page ST-48) instead of going into it here.

-Electrical issues that can cause PS problems.-

1. Check your power steering oil pressure switch. The FSM tells you to check the power steering oil pressure switch for 2-3 ohms of resistance between it's terminals when it is disconnected. What it doesn't tell you is that the switch is a normally open switch and that in order to see a resistance of 2-3 ohms it has to be closed. You must check the switch while the power steering system is together and while turning the steering wheel with the car running. The purpose of the switch is to tell the ECU when the power steering pressure has reached a certain point of pressure. When this happens the switch closes. The ECU detects that the switch is closed and raises the engine RPMs to allow the power steering pump to raise the PS oil pressure. This situation usually happens when the car is at a low idle or RPM.

2. Check the power steering solenoid (1990 FSM page ST-37, page ST-88). The power steering solenoid operation is dependant on vehicle speeds. The power steering solenoid reduces the amount of pressure that reaches the steering gear at higher road speeds. If the signal is lost or the solenoid is not working properly you may see a loss of road feel and/or increased steering sensitivity at highway speeds.

3. Check the steering wheel angle sensor (1990 FSM page and 1990 FSM page ST-57). If the sensor is bad or the sensor is loose it can cause erroneous signals to the PS system which will effect it's operation. These signals are sent to the HICAS/Power steering module.

4. Check the steering wheel neutral position switch (1990 FSM page ST-58). The steering wheel must be straight when driving in a straight line. If not, this will send erroneous signals to the PS system which will effect it's operation. These signals are sent to the HICAS/Power steering module.

5. One of the common causes of PS problems is the speed sensor. The speed sensor creates a wave forming pulse which is first sent to the speedometer in the gauge cluster. This signal is then sent to the speed signal input pin 53 at the ECU to calculate the speed. If the speedometer board in the gauge cluster is bad it is possible that although you may see an indicated speed on the speedometer, no signal or an intermittent signal is being sent from the speedometer board to the ECU. If the signal is lost for 10 or more seconds, a hard steering problem will occur. You can eliminate the possibility of a lost signal by using a consult software or a TechTom MDM-100 to monitor the speed signal. Using one of these options to monitor the speed signal monitors the signal after it has left the speedomter in the gauge cluster and has arrived at the ECU. Since the speed sensor is located in the transmission, you will need to monitor the speed signal while driving. You can simulate driving by placing the rear of the vehicle on jack stands so that the tires clear the floor.

-Twin turbo models-

The speed signal is used by the HICAS module which aids in controlling the power steering. The HICAS module is constantly monitoring the speed signal. The speed signal does not get to the HICAS module in the same way it gets to the ECU. The HICAS module has it's own micro controller just as the ECU does. This microcontroller is on the same bus with the ECU's microcontroller so the ECU can let the HICAS module know what's going on. This is where the HICAS module gets the speed information from.

The HICAS module has it's own self diagnostics (Self diagnosis, 1990 FSM page ST-68) which can be initiated to display fault codes of it's own. This can help to identify a problem with the HICAS module which may in turn be affecting the power steering system.

Note: In twin turbo models the power steering control module is part of the HICAS module and not a separate module. This is why when things go wrong with the HICAS signals the power steering can be effected. These modules are also very prone to circuit failures due to the deteriorating condition of the old solder connections.

The most common faults that have caused the Z32 PS system to fail are.

1. A bad speed sensor or it's wire circuit.

2. A bad speedometer, gauge cluster or it's wire circuit.

3. A bad HICAS/Power Steering Control Module or it's wire circuit.

4. Bad power steering switch or it's wire circuit.

5. Bad power steering solenoid or it's wire circuit.

If your PS system is currently working I highly recommend you do one simple thing. With your car parked, remove your battery negative cable and then unplug the connectors to your HICAS/Power steering module. Reconnect your battery and start your car. While parked, turn your steering wheel left to right and right to left. Think about what it feels like and how much force is needed to turn the steering wheel. You now know how it feels to have an electrical issue related to a power steering system problem. If you ever have a mechanical related problem with your power steering you will most likely find that it will be much harder for you to turn your steering wheel. Knowing how the electrical problem feels will help point you in the right direction in troubleshooting your PS system if a problem occurs.

I decided to do this write-up after solving what seemed to be a never ending problem with my own PS system. The information I learned here has solved my problems and I hope it helps to solve yours too. Thanks for reading!

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