P1738 – PRESSURE CONTROL SOLENOID “B” STUCK ON
Comprehensive Technical Guide for Automotive Professionals
Technical Definition and System Overview
System Architecture and Function
The Pressure Control Solenoid “B” (PCS-B) is a pulse-width modulated (PWM) electro-hydraulic actuator located within the transmission valve body assembly. This solenoid operates as a variable bleed control device that modulates line pressure by controlling hydraulic flow through precise orifice metering.
Operating Principles
PCS-B receives a duty cycle command from the Transmission Control Module (TCM) ranging from 0-100%. At 0% duty cycle, the solenoid is fully closed, allowing maximum line pressure. At 100% duty cycle, the solenoid is fully open, bleeding off pressure to the sump. The “stuck on” condition indicates the solenoid is electrically or mechanically locked in the fully open position, resulting in insufficient line pressure for proper clutch application.
Standard Circuit Configuration
Complete Diagnostic Procedure
Pre-Diagnostic Requirements
Required Equipment: Digital Multimeter (True RMS capable), Oscilloscope (100MHz minimum), OBD-II Scanner with bidirectional controls, Factory Service Manual, Transmission Pressure Gauge (0-300 PSI).
Safety Precautions: Disconnect negative battery terminal, allow transmission to cool below 50°C (122°F), use proper jack stands rated for vehicle weight.
Step-by-Step Electrical Diagnosis
2.1. Initial System Check
1. Battery Voltage Verification: Measure battery voltage with engine off (12.4V-12.8V) and with engine running (13.8V-14.8V).
2. Ground Circuit Integrity: Check chassis ground G102 (typically near transmission mount) and engine ground G201 for resistance (0.2Ω maximum).
2.2. Solenoid Circuit Testing
| Test Parameter | Specification | Acceptable Range | Failure Threshold | Test Procedure |
|---|---|---|---|---|
| Coil Resistance | 5.5Ω @ 20°C | 4.5Ω – 6.5Ω | < 3.5Ω or > 7.5Ω | Disconnect harness, measure between terminals |
| Insulation Resistance | > 10MΩ | > 1MΩ | < 500kΩ | Terminal to solenoid body @ 500VDC |
| Current Draw | 1.2A @ 50% DC | 1.0A – 1.4A | < 0.5A or > 2.0A | Series ammeter in circuit |
| PWM Frequency | 292Hz | 290Hz – 294Hz | < 280Hz or > 300Hz | Oscilloscope on signal wire |
| Voltage Drop | 0.3V max | 0.1V – 0.5V | > 1.0V | Circuit loaded @ 1A |
2.3. TCM Communication Verification
ID: 0x7E0 | DATA: 02 10 03 00 00 00 00 00
// TCM Response (Normal Operation)
ID: 0x7E8 | DATA: 06 50 03 00 32 00 00 00
// Byte 4: 0x32 = 50% Duty Cycle Command
Associated Error Codes and Cascading Faults
Primary Related DTCs
The following codes commonly appear concurrently with P1738, indicating systematic transmission control issues:
| DTC Code | Description | Relationship to P1738 | Diagnostic Priority |
|---|---|---|---|
| P0741 | Torque Converter Clutch Circuit Performance | Shared hydraulic circuit – 85% correlation | High |
| P0753 | Shift Solenoid “A” Electrical | Shared power supply circuit – 70% correlation | High |
| P0780 | Shift Malfunction | Result of pressure loss – 60% correlation | Medium |
| P0730 | Incorrect Gear Ratio | Secondary effect – 45% correlation | Medium |
| P1791 | Line Pressure Solenoid Circuit | Sibling solenoid circuit – 40% correlation | Medium |
| P2757 | Transmission Fluid Pressure Sensor Circuit | Feedback monitoring – 35% correlation | Low |
Manufacturer-Specific Technical Data
Resistance Specifications by Manufacturer
| Manufacturer | Transmission Model | Solenoid P/N | Resistance @ 20°C | Current @ 12V | Frequency | Notes |
|---|---|---|---|---|---|---|
| Honda/Acura | BAYA/MAYA | 28250-RBB-A01 | 5.5Ω ± 0.5Ω | 1.15A | 292Hz | Internal O-ring prone to swelling |
| Ford | CD4E | 7T4Z-7G491-A | 4.8Ω ± 0.3Ω | 1.25A | 300Hz | Check internal filter screen |
| GM | 4T45-E | 24236991 | 6.2Ω ± 0.4Ω | 0.98A | 285Hz | TSB 04-07-30-010 |
| Toyota | U340E | 35300-30100 | 5.1Ω ± 0.6Ω | 1.18A | 295Hz | Updated design 2015+ |
| Hyundai/Kia | A6LF1 | 46210-2E000 | 5.8Ω ± 0.4Ω | 1.05A | 290Hz | Recall 167 for harness chafing |
| Nissan | RE5R05A | 31706-31X0A | 4.5Ω ± 0.5Ω | 1.33A | 305Hz | Requires TCM reprogram after replacement |
Technical Service Bulletins (TSBs) Related to P1738
| TSB Number | Manufacturer | Date | Description | Affected Models |
|---|---|---|---|---|
| TSB 15-012 | Honda | 2019-03-15 | Updated solenoid design for improved heat resistance | 2016-2019 Odyssey, Pilot |
| TSB 14-7-3 | Ford | 2014-07-14 | Wiring harness chafing at transmission connector | 2013-2014 Escape 2.5L |
| TSB 08-07-30-006E | GM | 2020-08-10 | TCM software update for false P1738 detection | 2017-2020 Equinox, Terrain |
| TSB T-SB-0031-19 | Toyota | 2019-02-11 | Valve body assembly replacement procedure | 2018-2019 Camry, Avalon |
Mechanical Inspection and Pressure Testing
Hydraulic System Pressure Analysis
| Test Condition | Expected Pressure | P1738 Fault Pressure | Tolerance | Diagnostic Action |
|---|---|---|---|---|
| Park/Neutral @ 2000 RPM | 85-115 PSI | 40-60 PSI | ±10 PSI | Check solenoid mechanical operation |
| Drive @ 2000 RPM | 95-125 PSI | 45-70 PSI | ±15 PSI | Verify valve body sealing |
| Reverse @ 1500 RPM | 120-150 PSI | 55-85 PSI | ±20 PSI | Inspect accumulator pistons |
| 3-2 Downshift @ 3000 RPM | 180-220 PSI | 75-110 PSI | ±25 PSI | Check line pressure control valve |
5.1. Valve Body Inspection Points
1. Pressure Regulator Valve: Check for scoring on valve bore (maximum allowable: 0.003″ clearance).
2. Solenoid Mounting Surface: Verify flatness with straight edge (maximum deviation: 0.002″).
3. Filter Screen: Inspect for debris accumulation (typically metallic particles from clutch wear).
4. Transfer Plate Passages: Use compressed air (30 PSI maximum) to verify unrestricted flow.
Frequently Asked Technical Questions
Yes, approximately 28% of P1738 cases involve valve body mechanical faults. Common issues include:
- Stuck pressure control valve: Due to contamination or scoring in bore
- Worn valve body bore: Excessive clearance (>0.004″) allowing bypass
- Failed accumulator spring: Broken or collapsed spring affecting pressure modulation
- Transfer plate leakage: Warped plate or failed gasket allowing cross-leakage between circuits
Diagnostic tip: Perform air pressure testing on individual circuits before condemning the solenoid.
Three distinct oscilloscope patterns indicate PCS-B failure:
Expected: Clean PWM square wave @ 1.2A peak
Fault: Current ramps to 2.5A+ then drops suddenly
// Pattern 2: Intermittent Open Circuit
Expected: Consistent duty cycle modulation
Fault: Signal drops to 0V randomly for 2-50ms intervals
// Pattern 3: Shorted Coil
Expected: 5.5Ω resistance reflected in waveform
Fault: Current spike > 3.0A with collapsed magnetic field
Use current probe on oscilloscope Channel 1 and voltage probe on Channel 2 for comparative analysis.
Temperature significantly affects solenoid resistance and performance:
| Temperature (°C) | Copper Coil Resistance | Hydraulic Response Time | Maximum Duty Cycle | Failure Likelihood |
|---|---|---|---|---|
| -20 | 4.2Ω | 85ms | 85% | Low |
| 20 | 5.5Ω | 45ms | 100% | Low |
| 80 | 7.1Ω | 35ms | 92% | Medium |
| 120 | 8.8Ω | 55ms | 75% | High |
| 150 | 10.5Ω | 120ms | 60% | Critical |
Critical Note: Always test at operating temperature (80-100°C) for accurate diagnosis. Cold testing may miss temperature-sensitive failures.
Modern vehicles require specific recalibration procedures:
- TCM Reset and Relearn: Clear adaptive memory using factory scan tool
- Solenoid Current Learning: Most vehicles (2010+) require current draw calibration
- Pressure Sensor Zero-Point Calibration: Required on systems with pressure feedback
- Shift Adaptation Reset: Force TCM to relearn clutch fill times
Factory-specific procedures:
- Honda/Acura: HDS → AT → Shift Learning → Complete Procedure
- Ford: IDS → Module Programming → Parameter Reset → Transmission Adaptive Tables
- GM: GDS2 → Special Functions → Transmission Adaptive Values → Reset
- Toyota: Techstream → Powertrain → Transmission → Initialize
Failure to perform these procedures may result in harsh shifting and premature component wear.
