P1902

What Does Code P1902 Mean?

DTC P1902 signifies an detected intermittent short circuit within the control circuit of Pressure Control Solenoid “B” (PCS “B”) by the Powertrain Control Module (PCM), or in some applications, the Transmission Control Module (TCM). In modern automatic transmissions, Pressure Control Solenoids are electro-hydraulic actuators responsible for regulating transmission line pressure and modulating clutch application and release pressure. PCS “B” typically refers to a specific solenoid within the transmission’s valve body that controls a particular hydraulic circuit, often related to an input or output shaft speed sensor, or a specific clutch pack, depending on the transmission design.

The PCM/TCM continuously monitors the electrical resistance and current flow through the PCS “B” control circuit. When an intermittent short occurs, the module detects an unexpected drop in resistance or an abrupt increase in current that deviates from the calibrated operating parameters. This suggests a direct, though not constant, path for current to ground or sometimes to voltage, bypassing the solenoid’s intended impedance. This anomaly can disrupt the PCM’s ability to precisely control hydraulic pressure, leading to erratic transmission behavior. Because the fault is intermittent, the PCM registers it when the condition momentarily appears and disappears, indicating a transient electrical fault rather than a hard short.

Common Symptoms

• Harsh or Erratic Shifting: The most common symptom, as line pressure control is compromised.
• Transmission Slipping: Insufficient or incorrect hydraulic pressure can lead to clutches not engaging fully.
• Delayed Engagement: Noticeable lag when shifting from Park to Drive or Reverse.
• Transmission Overheating: Slipping clutches generate excessive heat.
• Reduced Fuel Economy: Due to increased engine load from slipping or improperly managed shifts.
• Transmission Entering Limp Mode: The PCM may engage a failsafe mode to prevent further damage, limiting available gears or engine power.
• Illuminated Malfunction Indicator Lamp (MIL): The Check Engine Light will be triggered.

What Causes the Code P1902?

• Faulty Pressure Control Solenoid “B”: An internal short circuit within the solenoid winding itself, often due to insulation breakdown or manufacturing defect.
• Damaged or Chafed Wiring Harness: The wiring leading to or from PCS “B” may intermittently short to ground or to another power/signal wire due to rubbing against sharp edges, heat, or vibration.
• Corroded or Loose Electrical Connector Pins: Corrosion on the solenoid or PCM/TCM connector pins, or a loose pin fit, can create an intermittent short circuit path or an unstable connection that mimics a short.
• Contaminated Transmission Fluid: While not a direct cause, severely contaminated fluid with metallic debris can potentially bridge internal electrical contacts or cause mechanical issues that stress the solenoid, leading to internal electrical failure.
• Internal Transmission Short: Less common, but a short could occur within the transmission’s internal wiring harness, valve body housing, or even the circuit board (if applicable) where the solenoid connects.
• Faulty Transmission Control Module (TCM/PCM): Rare, but an internal short within the module’s driver circuit for PCS “B” could intermittently occur.

How to Diagnose and Troubleshoot

Diagnosing an intermittent short requires meticulous inspection and electrical testing. A digital multimeter (DMM) and an advanced OBD-II scanner capable of reading live transmission data are essential.

1. Verify Code and Gather Data: Connect an OBD-II scanner and confirm P1902. Check for any other related transmission DTCs. Review freeze frame data to understand operating conditions when the code was set (transmission temperature, engine speed, gear, etc.). Clear the code and attempt to replicate the failure conditions.
2. Visual Inspection of Transmission Fluid: Check the transmission fluid level and condition. Note any burnt smell, dark coloration, or metallic debris, which could indicate internal transmission damage that might stress solenoids.
3. Thorough Wiring Harness and Connector Inspection:
   • Visually inspect the entire wiring harness leading to the transmission and specifically to the PCS “B” connector (if externally accessible). Look for signs of chafing, pinching, rubbing, or heat damage. Pay close attention to areas near exhaust components, sharp edges, and frame rails.
   • Inspect the electrical connectors at the transmission and the PCM/TCM. Look for bent, corroded, pushed-out, or spread pins. Ensure all connections are secure. A “wiggle test” on the connectors while monitoring with a DMM can sometimes reveal intermittent faults.
4. Electrical Resistance Test of Solenoid “B”:
   • Locate PCS “B.” This often requires dropping the transmission pan and removing the valve body to gain access. Consult a vehicle-specific service manual for exact location and procedures.
   • Disconnect the electrical connector from PCS “B.” Using a DMM set to ohms, measure the resistance across the two terminals of the solenoid itself. Compare this reading to manufacturer specifications (typically 10-30 ohms for most pressure control solenoids). An intermittently very low reading (close to 0 ohms) or an unstable reading that fluctuates significantly when wiggling the solenoid or its internal wiring indicates an internal short.
   • While still disconnected, measure the resistance from each solenoid terminal to the transmission case/chassis ground. Both readings should be infinite (OL – Open Line). Any low resistance reading indicates a short to ground within the solenoid.
5. Circuit Integrity Test (Wiring Harness):
   • With the PCS “B” disconnected and the PCM/TCM connector also disconnected, use your DMM to check the resistance of the wiring harness for the PCS “B” circuit. Measure between the corresponding pins at the PCM/TCM harness connector and the PCS “B” harness connector. Verify continuity and resistance within specification (typically < 1 ohm).
   • Now, measure the resistance from each wire of the PCS “B” circuit at the PCM/TCM harness connector to chassis ground. Both readings should be infinite (OL). An intermittent low resistance reading here indicates a short to ground in the wiring harness.
   • Similarly, check for a short to vehicle power by checking voltage between the PCS “B” wires and a known power source with the ignition on. It should be 0V.
   • Perform a “wiggle test” on the harness while measuring resistance to ground. Flex, pull, and twist the harness along its entire length, especially at bends and tie-down points, to see if the resistance reading fluctuates or briefly drops.
6. PCM/TCM Diagnosis (If all else fails): If the solenoid and wiring harness test perfectly, and the intermittent short persists, consider the possibility of a faulty PCM/TCM. This is rare and should only be pursued after exhaustively ruling out all other causes. Specific diagnostic procedures for the PCM’s output drivers for PCS “B” would be required, as per the service manual.

Recommended Repairs and Solutions

Once the source of the intermittent short is identified through the diagnostic steps, the repair focuses on replacing or repairing the faulty component:

• Replace Pressure Control Solenoid “B”: If the solenoid itself tests faulty, it will need to be replaced. This typically involves draining the transmission fluid, dropping the transmission pan, and removing the valve body (or components attached to it) to access the solenoid. Always use an OEM or high-quality aftermarket solenoid to ensure proper function and longevity.
• Repair or Replace Damaged Wiring Harness: If the wiring harness is found to be shorting intermittently, the damaged section must be repaired or replaced. For repairs, use appropriate gauge wire, solder connections, and seal with heat-shrink tubing. Ensure the repaired section is routed away from any potential rubbing or heat sources. In cases of extensive damage, replacing the entire engine/transmission harness may be necessary.
• Clean and Secure Electrical Connectors: If corrosion or loose pins are identified, use electrical contact cleaner and a small pick or terminal tool to carefully clean and restore proper tension to the connector pins. Apply dielectric grease to prevent future corrosion.
• Transmission Fluid and Filter Service: Any time the transmission pan is dropped, it is highly recommended to perform a transmission fluid and filter service. Use the manufacturer-specified fluid type and quality. This helps ensure optimal transmission health and prevents issues caused by old or contaminated fluid.
• PCM/TCM Replacement: If after all other components have been thoroughly tested and verified as functional, the PCM/TCM is implicated, it will need to be replaced and potentially programmed to the vehicle. This is a complex and often expensive repair, so it should be a last resort.

Mechanic’s Tips: Always consult the specific vehicle’s service manual for torque specifications, solenoid resistance values, and proper transmission fluid fill procedures. When working inside the transmission, maintain a clean environment to prevent contamination. After any transmission repair, it’s often beneficial to perform a transmission adaptive learning procedure using an advanced scan tool to allow the PCM/TCM to relearn optimal shift points and pressures.