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Electronic Steering System: Diagnosis Mercury Sable III

Electronic Steering 5 illustrations ~1433 words

TROUBLE SHOOTING

Note. A New Generation Star (NGS) Tester (007-00500) or equivalent is required for testing the VAPS system.

Before performing individual component or system tests, check the following for possible cause of system malfunction.

  1. Tire Pressure
  2. Mechanical Condition Of Steering
  3. Power Steering Fluid Level
  4. Pump Pressure
  5. Faulty Fuse No. 8, 20 Or 23
  6. Loose Or Corroded Connectors
  7. Damaged Wiring

If problem remains after inspection, connect and operate New Generation Star (NGS) Tester (007-00500) following manufacturer's instructions. Perform data link diagnostics test. See MODULE COMMUNICATIONS NETWORK article in the ACCESSORIES/SAFETY EQUIPMENT section. If scan tool displays NO RESPONSE/NOT EQUIPPED for Generic Electronic Module (GEM), go to TEST A: NO COMMUNICATION WITH GEM .

If GEM passes data link diagnostics test, retrieve and record continuous Diagnostic Trouble Codes (DTCs) and perform on-demand self test vehicle dynamics module to retrieve current DTCs. See MODULE COMMUNICATIONS NETWORK article in the ACCESSORIES/SAFETY EQUIPMENT section.

HYDRAULIC SYSTEM PRESSURE TEST

  1. Reservoir must be kept full and at normal operating temperature during testing. Connect Power Steering System Analyzer (014-00207) between pressure line and pump, with gauge between pump and tester valve. Start and idle engine for 2 minutes.
  2. With engine idling and fluid hot, record pressure and flow with tester valve open. If flow is less than 1.5 gals. (5.7L) per minute, pump may require service. However, proceed with testing at this point.
  3. If idle pressure is greater than 150 psi (10.5 kg/cm 2 ), check hoses for restrictions. Partially close tester valve. Allow pressure to increase to 740 psi (52 kg/cm 2 ). Record flow. If flow is less than 1.4 gal/min. @ 740 psi (5.3L/min. @ 5100 kPa), replace pump.
  4. Close and partially open tester valve 3 times. Tester valve must not remain closed more than 5 seconds. Observe and record pressure each time valve is closed. If readings differ more than 50 psi (3.5 kg/cm 2 ), flow control valve may be sticking. If relief pressure (valve closed) is less than 1200 psi (9520 kPa), replace power steering pump.
  5. Increase engine speed to about 1500 RPM. Observe and record flow. If flow exceeds 2.7 gal/min. (10.2L/min.), replace power steering pump.
  6. Return engine to idle speed. Turn wheel from stop to stop. Observe and record flow at both stops. Pressure should be 1200-1380 psi (8275-9520 kPa). Flow should drop to less than .5 gal. (1.9L) per minute. If pressure fails to reach maximum or if flow does not drop to less than .5 gal. (1.9L) per minute, internal leakage of steering gear exists. Replace steering gear.

TEST A: NO COMMUNICATION WITH GEM

  1. Check Power Circuit To GEM - Remove fuse No. 23 (5-amp) from fuse junction panel. Measure resistance between output terminal of fuse cavity No. 23 and ground. Resistance reading should start at more than 1 M/ohms and drop to less than 3 k/ohms. If resistance is within specification, go to step 7). If resistance is not within specification, go to next step.
  2. Check Resistance Connect ohmmeter as in step 1). If resistance is less than 10 ohms, go to step 4). If resistance is not less than 10 ohms, go to next step.
  3. Check GEM Disconnect GEM connector C201 from fuse junction panel. (Scheme 6) Disconnect ohmmeter and reconnect ohmmeter as in step 1). Resistance reading should start at more than one M/ohms and drop to less than 3 k/ohms. If resistance is within specification, replace GEM. Check system operation. If resistance is not within specification, go to next step.
  4. Check Fuse Panel Disconnect 33-pin connector from fuse junction panel. Measure resistance between fuse cavity No. 23 and ground. If resistance is less than 10 k/ohms, replace fuse junction panel. If resistance is greater than 10 k/ohms and vehicle is equipped with Passive Anti-Theft System (PATS) or Remote Anti-Theft (RAP) system, go to next step. If resistance is greater than 10 k/ohms and vehicle is not equipped with Passive Anti-Theft System (PATS) or Remote Anti-Theft (RAP) system, go to step 7).
  5. Check PATS Module Disconnect PATS module harness connector. Disconnect and reconnect ohmmeter as in step 1). Resistance reading should start at more than one M/ohms and drop to less than 3 k/ohms. If resistance is within specification, replace PATS module. Check system operation. If resistance is not within specification, go to next step.
  6. Check RAP Module Disconnect RAP module connector C254. (Scheme 7) Disconnect and reconnect ohmmeter as in step 1). If resistance is greater than one M/ohms, replace RAP module. Check system operation. If resistance is less than one M/ohms, repair short to ground in circuit No. 1001 (White/Yellow wire) between fuse panel and control module(s).
  7. Check Power Grounds Disconnect GEM connector C248. (Scheme 8) Measure resistance between ground and GEM harness connector C248 (Gray 26-pin connector) pins No. 14 and 25 (Black wires). If resistance is less 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open ground (Black wire). Check system operation.
  8. Check Dedicated Ground Disconnect GEM connector C223 (Gray 22-pin connector). (Scheme 7) Measure resistance between C223 pin No. 12 (Black/White wire). If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, repair open ground (Black/White wire).
  9. Check Start & Run Circuit Disconnect GEM connector C236 (Gray 16-pin connector). (Scheme 5) Turn ignition on. Measure voltage between ground and C236 pin N o. 14 (Red/Yellow wire). If battery voltage exists, go to step 11). If battery voltage does not exist, go to next step.
  10. Check Fuse No. 12 Remove and check fuse No. 12 (5-amp). If fuse is okay, repair open Red/Yellow wire between fuse panel and GEM. If fuse is blown, repair short to ground in Red/Yellow wire between fuse panel and GEM. Check system operation.
  11. Check Black/Light Green Wire Disconnect GEM connector C223 (Gray 22-pin connector). Measure resistance between C223 pin No. 22 (Black/Light Green wire) and ground. If resistance is less than 5 ohms, a fault exists in ISO 9141 communication link (circuit No. 70). If resistance is greater than 5 ohms, repair open Ground (Black/Light Green wire).

Scheme 5

Scheme 5
Scheme 5

Scheme 6

Scheme 6
Scheme 6

Scheme 7

Scheme 7
Scheme 7

Scheme 8

Scheme 8
Scheme 8

TEST B: STEERING EFFORT DOES NOT VARY WITH VEHICLE SPEED

  1. CHECK VSS PID - Install New Generation Star (NGS) tester or equivalent. Access VSS_GEM PID. Test drive vehicle while observing VSS_PID. If PID value does not indicate correct vehicle speed, go to next step. If PID value indicates correct vehicle speed, perform on-demand self test. If any DTCs are retrieved, repair as necessary. If No DTCs exist and symptom remains, fault is mechanical in nature. Repair as necessary.
  2. Check Gray/Brown Wire For Open Disconnect Vehicle Speed Sensor (VSS). Disconnect fuse junction panel C225 (Black 22-pin connector). (Scheme 9) Measure resistance of Gray/Brown wire between fuse junction panel Connect C225 and VSS harness connector. If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, repair open Gray/Brown wire.
  3. Check Gray/Brown Wire For Short To Ground Measure resistance between C225 pin No. 7 (Gray/Brown wire) and ground. If resistance is greater than 10 k/ohms, go to next step. If resistance is less than 10 k/ohms, repair short to ground in Gray/Brown wire.
  4. Check Gray/Brown Wire For Short To Power Measure voltage between C225 pin No. 7 (Gray/Brown wire) and ground. If battery voltage does not exist, go to next step. If battery voltage exists, repair short to power in Gray Brown wire. Check system operation.
  5. Check Fuse Panel For Open Disconnect GEM module connector C201 (19-pin) from fuse junction panel. Measure resistance between C201 pin No. 9 and C225 pin No. 7. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, replace fuse junction panel. Check system operation.
  6. Check Fuse Junction Panel For Short Disconnect GEM from fuse junction panel. Turn ignition on. Measure voltage between fuse panel connector C201 pin No. 9 and ground. If battery voltage does not exist, go to next step. If battery voltage exists, replace internally shorted fuse junction panel.
  7. Check Fuse Junction Panel For Short To Ground Measure resistance between fuse junction panel connector C201 and ground. If resistance is less than 10 k/ohms, replace fuse junction panel. If resistance is greater than 10 k/ohms, replace vehicle speed sensor. Restore electrical connections and check system operation.

Scheme 9

Scheme 9
Scheme 9

Cleaning & Inspection

Clean rack and housing bore. Check steering gear housing for cracks or leakage. If steering gear is damaged, replace with a new unit. Inspect bellows for cracking or signs of dryness. Check clamps for damage or corrosion. Replace bellows and clamps as necessary.

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