What Does P0959 Mean?
The transmission control module (TCM) has detected an intermittent electrical signal in the auto shift manual (ASM) mode circuit, which allows the driver to manually select gears via a shift lever or paddle shifters. This intermittent condition means the circuit is making and breaking contact unpredictably, causing the manual shift mode to work erratically or cut out momentarily. The driver may notice the transmission unexpectedly switching between manual and automatic modes, or the manual shift function may fail to engage consistently.
Common Causes
35%
Loose or corroded connector at the gear selector/shifter assembly
30%
Intermittent break in wiring harness between shifter and TCM due to chafing or fatigue
20%
Failing manual mode position switch or contact assembly in the shifter
10%
Poor ground connection at the TCM or shifter assembly
5%
Faulty TCM internal driver circuit for manual mode input
Diagnostic Steps
1
Retrieve freeze frame data to identify the operating conditions (vehicle speed, gear position, temperature) when the intermittent fault occurs.
2
Inspect the gear selector/shifter assembly connector for corrosion, bent pins, looseness, or water intrusion. Wiggle the connector while monitoring the manual mode PID on the scan tool to reproduce the intermittent.
3
Perform a wiggle test on the wiring harness from the shifter to the TCM, paying close attention to areas where the harness passes through bulkheads, over sharp edges, or near heat sources. Monitor the manual mode circuit signal during the test.
4
Measure the resistance of the manual mode switch in each position — values should be stable and within specification. Any fluctuation or erratic readings indicate a failing switch.
5
If the harness and switch test good, back-probe the TCM connector and monitor the signal voltage while actuating the manual shift mode repeatedly to isolate whether the fault is at the TCM end.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
The transmission control module (TCM) has detected an intermittent electrical signal in the auto shift manual (ASM) mode circuit, which allows the driver to manually select gears via a shift lever or paddle shifters. This intermittent condition means the circuit is making and breaking contact unpred...
The most common cause of P0959 (Auto Shift Manual Mode Circuit Intermittent) is: Loose or corroded connector at the gear selector/shifter assembly
Typical repair costs for P0959 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle can still be driven in normal automatic mode. However, the unpredictable behavior of the manual shift function could be distracting. Avoid relying on manual mode for engine braking on steep grades until the intermittent is resolved.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0959 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Automatic Transmission / Transaxle
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
