Speed Dependent Steering System - Evo Chevrolet Chevy Van G2500

DESCRIPTION & OPERATION

Note. For repair procedures not covered in this article, see STEERING SYSTEM - POWER RECIRCULATING BALL article.

The Electronic Variable Orifice (EVO) power steering system consists of the following

1. Power steering pump, outlet and return hoses, steering box and linkage.
2. Power steering fluid flow actuator, mounted on pump.
3. Power Steering Control Module (PSCM), mounted under instrument panel.
4. Steering Wheel Position (SWP) sensor, mounted in lower bearing of steering column.
5. Powertrain Control Module (PCM) (diesel only), mounted in center of instrument panel.
6. Vehicle Control Module (VCM) (gasoline only), mounted in left side of engine compartment.

The system increases or decreases the amount of fluid leaving the power steering pump. Outlet hose has a check valve to prevent kickback on some models. When vehicle is stopped or moving at low speeds, system allows full hydraulic fluid flow for maximum assist. As vehicle speed increases, a variable orifice closes at pump, reducing fluid flow to improve road feel and directional stability. Flow ranges from 3.5 gallons per minute at idle to .7 gallon per minute at speed.

Steering Wheel Position (SWP) sensor detects rapid movement when defensive maneuvers are made. PSCM uses this sensor input to adjust the current to fluid flow actuator. If PSCM detects a fault, EVO system is disabled, allowing maximum power assist. When ignition is turned off and vehicle is restarted, PSCM resets and allows EVO operation until it detects another fault. PSCM has self-diagnostics and stores diagnostic trouble codes. See DIAGNOSIS & TESTING . Codes will clear after 100 ignition cycles without fault.

Note. When replacing PSCM, EEPROM inside must be calibrated using special equipment.

GENERAL PRECAUTIONS

SYSTEM PRECHECK

Check fluid for correct type, level and contamination. Check PSCM, fluid flow actuator and wiring for damage or corrosion. Check power steering system for poor performance and leaks. Check speedometer operation to verify VSS signal.

SELF-DIAGNOSTICS

PSCM monitors system and can set Diagnostic Trouble Codes (DTCs). Codes are retrieved and cleared using scan tool. Disconnecting PSCM or battery will not clear codes.

DIAGNOSTIC SYSTEM CHECK

1. Connect scan tool. Turn ignition on. Check for stored codes. If codes exist, go to appropriate TEST. See «EVO TEST INDEX»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo) . If no codes exist, go to next step.
2. Using scan tool, monitor steering wheel position sensor and fluid flow actuator parameters. This verifies communication between PSCM and VCM. If parameters exist, go to step 8). If parameters do not exist, go to next step.
3. Check fuse No. 21 (20-amp). If fuse is okay, go to step 5). If fuse is bad, go to next step.
4. Check connectors and circuit between fuse 21 and PSCM connector terminal B8. If short to ground is found, repair short and go to step 11). If no short is found, go to step 8).
5. Check fuse No. 4 (10-amp). If fuse is okay, go to step 7). If fuse is bad, go to next step.
6. Check connectors and circuit between fuse No. 4 and PSCM connector terminal B3. If short to ground is found, repair short and go to step 11). If no short is found, go to step 8).
7. Disconnect PSCM connector. Check continuity between PSCM connector terminal B4 and ground. If continuity exists, go to step 12). If continuity does not exist, repair circuit. Go to next step.
8. Check continuity between PSCM terminal B1 and ground. If continuity exists, go to step 10). If continuity does not exist, repair circuit. Go to step 11).
9. Using scan tool, monitor steering wheel position sensor and fluid flow actuator parameters. Turn steering wheel 90 degrees left, then 90 degrees right. If scan tool values change as wheel is turned, go to next step. If values do not change, go to step 11).
10. System is normal. Go to step 11).
11. Clear codes. Test drive vehicle at normal operating temperatures. Retrieve codes. If no codes exist, system is normal. If codes exist, go to appropriate test. See «EVO TEST INDEX»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo) .

TESTING

EVO TEST INDEX

Diagnostic Aids

PSCM calibrations are stored in EEPROM (Electronically Erasable Programmable Read Only Memory) in PSOM. If any calibration faults are detected, or no calibrations are programmed, code will set. EEPROM is not removable, entire PSCM must be replaced.

1. Ensure Diagnostic System Check was performed. If Diagnostic System Check was performed, go to next step. If Diagnostic System Check was not performed, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
2. If PSCM was previously installed, go to next step. If PSCM was not replaced, go to step 4).
3. Turn ignition off, then on. Clear codes. If DTC B0605 resets, go to step 5). If DTC B0605 does not reset, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
4. Check PSCM EEPROM I/D number. If number is 0000 (not programmed), go to step 3). If a valid number is set, go to next step.
5. Replace PSCM. Go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .

Code sets when PSCM detects a difference of more than 6 MPH between data line information and VSS input from VCM (gasoline only) or PCM (diesel only). See WIRING DIAGRAMS .

1. Ensure Diagnistic System Check was performed. If Diagnostic System Check was performed, go to next step. If Diagnostic System Check was not performed, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
2. Check codes. If any PCM or VCM VSS codes are set, go to step 4). If no other VSS codes are set, go to next step.
3. Check speedometer and cruise control operation. If speedometer and cruise control work properly, go to step 7). If speedometer and cruise control do not work properly, go to step 5).
4. Diagnose and repair DTCs. See appropriate TESTS W/CODES article in ENGINE PERFORMANCE section. Refer to menu below. G - TESTS W/CODES - 4.3L G - TESTS W/CODES - 5.0L G - TESTS W/CODES - 5.7L G - TESTS W/CODES - 6.5L G - TESTS W/CODES - 7.4L Clear codes. Go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
5. Diagnose and repair VSS problem. See appropriate TESTS W/CODES article in ENGINE PERFORMANCE section. Clear codes. Refer to menu above. Go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
6. Check circuit No. 1807 (Purple wire) for open, intermittent or poor connection at terminal B4 of PSCM connector. If no problem was found, go to step 8). If problem was found and repaired, go to step 9).
7. Check circuit No. 817 (Dark Green/White wire) for open, intermittent or poor connection at terminal A8 of PSCM connector. If no problem was found, go to step 6). If problem was found and repaired, go to step 9).
8. Replace PSCM. Go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
9. Turn ignition off. Reinstall all removed connectors/components. Clear all codes. Drive vehicle over 20 MPH for at least 20 seconds. If DTC C0100 resets, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .

Code sets when PSCM detects an open or short to ground or power on fluid flow actuator circuits No. 1294 (White wire) or No. 1295 (Brown wire). See WIRING DIAGRAMS .

1. Ensure Diagnostic System Check was performed. If Diagnostic System Check was performed, go to next step. If Diagnostic System Check was not performed, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
2. Turn ignition off. Connect scan tool and go to chassis section. Check for Codes C0502 and C0503. If either code is set, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) . If Codes C0502 and C0503 are not set, go to next step.
3. Connect scan tool and go to CHASSIS on scan tool. Command solenoid to 0, 25, 50, 75, and 100 percent ranges. Compare commanded and actual state of solenoid. If values are equal, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) . If values are not equal, go to next step.
4. Turn ignition off. Disconnect PSCM connector. Disconnect fluid flow actuator connector. Turn ignition on. Check voltage at terminals A1 and A3. If voltage exists, go to next step. If voltage does not exist, go to step 6).
5. Repair short to power on circuit No. 1294 (White wire) or No. 1295 (Brown wire). Go to step 9). If short was not found, go to step 8).
6. Turn ignition off. Disconnect PSCM connector. Disconnect fluid flow actuator connector. Check continuity between ground and terminals A1 and A3. If continuity exists, go to next step. If continuity does not exist, go to step 8).
7. Repair short to ground on circuit No. 1294 (White wire) or No. 1295 (Brown wire). Go to step 9). If short was not found, go to step 8).
8. Problem is intermittent. Clear codes and go to INTERMITTENT DIAGNOSIS.
9. Turn ignition off. Reinstall all removed connectors/components. Clear all codes. Go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .

Intermittent Diagnosis

Intermittent fault testing requires duplicating circuit or component failure to identify fault. To reproduce conditions causing intermittent fault, use following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Drive vehicle in similar conditions to fault occurrence.

Monitor circuit while attempting to reproduce condition.

Code sets when PSCM detects an open or short to ground on fluid flow actuator circuits No. 1294 (White wire) or No. 1295 (Brown wire) or there is no voltage for one second or longer. See WIRING DIAGRAMS .

1. Ensure Diagnostic System Check was performed. If Diagnostic System Check was performed, go to next step. If Diagnostic System Check was not performed, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
2. Turn ignition off. Disconnect fluid flow actuator connector. Check resistance between terminals of fluid flow actuator. If resistance is not 7-15 ohms, go to step 5). If resistance is 7-15 ohms, go to next step.
3. Turn ignition off. Disconnect fluid flow actuator connector. Check continuity between both terminals of fluid flow actuator and ground. If continuity exists, go to step 5). If continuity does not exist, go to next step.
4. Turn ignition off. Disconnect fluid flow actuator connector. Disconnect PSCM connector. Check continuity between ground and connector terminals A1 and A3. If continuity exists, go to step 6). If continuity does not exist, go to step 7).
5. Replace fluid flow actuator. Go to step 9).
6. Repair short to ground on circuit No. 1294 (White wire) or No. 1295 (Brown wire). Go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
7. Check fluid flow actuator connector and harness for intermittent short to ground. If no problem was found, go to step 9). If short was found, repair and go to next step.
8. Replace PSCM. Go to next step.
9. Turn ignition off. Reinstall all removed connectors/components. Clear all codes. Go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .

Code sets when PSCM detects a short to power on fluid flow actuator circuits No. 1294 (White wire) or No. 1295 (Brown wire) or voltage is greater than 12 volts for one second or longer. See WIRING DIAGRAMS .

1. Ensure Diagnostic System Check was performed. If Diagnostic System Check was performed, go to next step. If Diagnostic System Check was not performed, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .
2. Turn ignition off. Disconnect PSCM connector. Turn ignition on. Check voltage at connector terminals A3 and A1. If more than one volt exists, go to next step. If less than one volt exists, go to step 7).
3. Turn ignition off. Disconnect fluid flow actuator connector. Disconnect PSCM connector. Turn ignition on. Check voltage at connector terminals. If less than one volt exists, go to next step. If more than one volt exists, go to step 5).
4. Turn ignition off. Disconnect fluid flow actuator connector. Check resistance between terminals of fluid flow actuator. If resistance is not 7-15 ohms, go to step 6). If resistance is 7-15 ohms, go to step 7).
5. Repair short to power on circuit No. 1294 (White wire) or No. 1295 (Brown wire). Go to step 9).
6. Replace fluid flow actuator. Go to step 9).
7. Check fluid flow actuator connector and harness for intermittent short to power. If no problem was found, go to next step. If short was found, repair and go to step 9).
8. Replace PSCM. Go to next step.
9. Turn ignition off. Reinstall all removed connectors/components. Clear all codes. Go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) .

PSCM supplies 5-volt reference signal to sensor. Sensor return voltage varies between .2 volt (wheel straight) and 4.9 volts (1/4 turn). Code sets when PSCM detects circuit voltage less than .2 volt for more than one second. See WIRING DIAGRAMS .

1. Ensure Diagnostic System Check was performed. If Diagnostic System Check was performed, go to next step. If Diagnostic System Check was not performed, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) . Check sensor for damage, binding and grinding.
2. Turn ignition on. Connect scan tool. Select SWP display on scan tool. Check reading while turning steering wheel 1/4 turn, then back to straight ahead. Repeat in both directions. If voltage varies between .2 volt (wheel straight) and 4.9 volts (1/4 turn), go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) . If voltage is not as specified, go to next step.
3. Using scan tool Freeze Frame, repeat step 2). If voltage is less than .2 volt at any time, go to next step. If voltage is more than .2 volt at all times, go to step 12).
4. Disconnect SWP sensor. Jumper sensor signal circuit No. 1059 (Light Blue wire) and 5-volt reference circuit No. 705 (Gray wire) at sensor connector. Check scan tool SWP reading. If reading is more than 4 volts, go to step 10). If reading is less than 4 volts, go to next step.
5. Using Digital Multi-Meter (J39200), connect positive lead to battery positive. Connect meter negative lead to sensor signal circuit No. 1059 (Light Blue wire). This simulates a high signal return to check for an open circuit. Check scan tool SWP reading. If reading is more than 4 volts, go to next step. If reading is less than 4 volts, go tostep 8).
6. Check 5-volt reference signal circuit No. 705 (Gray wire) for open or short to ground. If circuit is okay, go to next step. If circuit is open or shorted to ground, repair circuit and go to step 12).
7. Check 5-volt reference signal circuit No. 705 (Gray wire) for poor connection at PSCM. If connection is okay, go to step 11). Repair connection if needed, and go to step 12).
8. Check sensor signal circuit No. 1059 (Light Blue wire) for open or short to ground. If circuit is okay, go to next step. If circuit is open or shorted to ground, repair circuit and go to step 12).
9. Check sensor signal circuit No. 1059 (Light Blue wire) for poor connection at PSCM. If connection is okay, go to step 11). Repair connection if needed, and go to step 12).
10. Replace SWP sensor. Go to step 12).
11. Replace PSCM. Go to step 12).
12. Clear codes. Test drive vehicle. Retrieve codes. If Code C0507 is not reset, go to next step. If Code C0507 is reset, go to step 2).
13. Check codes. If any codes are set, go to appropriate test. See «EVO TEST INDEX»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo) . If no codes are set, system is normal.

PSCM supplies 5-volt reference signal to sensor. Sensor return voltage varies between .2 volt (wheel straight) and 4.9 volts (1/4 turn). Code sets when PSCM detects circuit voltage more than 4.9 volts for more than one second. See WIRING DIAGRAMS .

1. Ensure Diagnostic System Check was performed. If Diagnostic System Check was performed, go to next step. If Diagnostic System Check was not performed, go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) . Check sensor for damage, binding and grinding.
2. Turn ignition on. Connect scan tool. Select SWP display on scan tool. Check reading while turning steering wheel 1/4 turn, then back to straight ahead. Repeat in both directions. If voltage varies between .2 volt (wheel straight) and 4.9 volts (1/4 turn), go to «DIAGNOSTIC SYSTEM CHECK»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo__diagnostic-system-check) . If voltage is not as specified, go to next step.
3. Using scan tool Freeze Frame, repeat step 2). If voltage is more than 4.9 volts at any time, go to next step. If voltage is less than 4.9 volts at all times, go to step 12).
4. Disconnect SWP sensor. Check reading. If voltage is more than .2 volt, go to step 6). If voltage is less than .2 volt, go to next step.
5. Using Digital Multi-Meter (J39200), connect positive lead to battery positive. Connect meter negative lead to sensor signal circuit No. 1059 (Light Blue wire). This checks for high resistance in circuit. Check scan tool SWP reading. If reading is more than 10 volts, go to step 7). If reading is less than 10 volts, go to step 9).
6. Check sensor signal circuit No. 1059 (Light Blue wire) for short to power. If circuit is okay, go to step 11). If circuit is shorted to power, repair circuit and go to step 12).
7. Check sensor signal circuit No. 1059 (Light Blue wire) for short to power. If circuit is okay, go to step 8). If circuit is shorted to power, repair circuit and go to step 12).
8. Check connections at SWP sensor. If connections are okay, go to step 10). If connections are bad, repair connections. Go to step 12).
9. Check sensor return circuit No. 1057 (Orange/Black wire) for open circuit. If circuit is okay, go to next step. If circuit is open, repair circuit. Go to step 12).
10. Replace SWP sensor. Go to step 12).
11. Replace PSCM. Go to step 12).
12. Clear codes. Test drive vehicle. Retrieve codes. If Code C0508 is not reset, go to next step. If Code C0508 is reset, go to step 2).
13. Check codes. If any codes are set, go to appropriate test. See «EVO TEST INDEX»(/chevrolet/chevy-van-g2500/1996-1998/remont/electronic-steering/#speed-dependent-steering-system-evo) . If no codes are set, system is normal.

Removal & Installation

Raise and support vehicle. Remove hose from actuator. (Scheme 1) Note position of wiring connector and remove. Move cooler lines as needed and remove actuator from pump. To install, reverse removal procedure. Tighten fasteners to specification. See TORQUE SPECIFICATIONS. Fill pump reservoir. Bleed system.

Scheme 1

POWER STEERING CONTROL MODULE (PSCM)

Disconnect negative battery cable. Disconnect wiring connectors. Remove PSCM. To install, reverse removal procedure.

Note. When replacing PSCM, EEPROM inside must be calibrated using special equipment.

STEERING WHEEL POSITION SENSOR

Steering column must be removed from vehicle to access steering wheel position sensor, located at bottom of column. See STEERING SYSTEM - POWER RECIRCULATING BALL article.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

Electronic Power Steering Wiring Diagram (Express & Savana). Scheme 2

See also:
• DIAGNOSIS & TESTING
• DIAGNOSTIC SYSTEM CHECK
• TORQUE SPECIFICATIONS