What Does P0956 Mean?
DTC P0956 indicates the ASM mode selection circuit is not performing within expected parameters. The TCM can communicate with the mode switch but receives signals that do not match any defined mode position, or the transition between modes is not clean. This often points to a worn switch with degraded detent positions or a resistor network that has drifted out of specification.
Common Causes
35%
Mode selector switch with worn detent positions or dirty contacts
20%
Resistor ladder in the mode switch circuit drifted out of range
20%
High-resistance connection at the switch connector altering signal levels
15%
Spilled liquid contamination on the mode switch mechanism
10%
Aftermarket switch or wiring modification incompatible with TCM calibration
Diagnostic Steps
1
Step 1: Monitor the mode switch signal voltage on a scan tool while cycling through all mode positions. Each position should produce a distinct, stable voltage level.
2
Step 2: Check for unstable or overlapping voltage readings between mode positions that would confuse the TCM. This indicates a worn switch or contaminated contacts.
3
Step 3: Inspect the mode switch for signs of liquid contamination, worn detents, or physical damage. Clean with electrical contact cleaner if contaminated.
4
Step 4: Measure the switch resistance values in each position and compare to manufacturer specifications. Out-of-range values confirm a failing switch.
5
Step 5: Replace the mode selector switch if resistance values are out of specification. Clear codes and verify each mode position is correctly recognized by the TCM.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
DTC P0956 indicates the ASM mode selection circuit is not performing within expected parameters. The TCM can communicate with the mode switch but receives signals that do not match any defined mode position, or the transition between modes is not clean. This often points to a worn switch with degrad...
The most common cause of P0956 (Auto Shift Manual Mode Circuit Range/Performance) is: Mode selector switch with worn detent positions or dirty contacts
Typical repair costs for P0956 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Performance issues with the mode circuit may cause the TCM to misidentify the selected mode or refuse to accept mode changes. The transmission will continue to operate but may not respond to driver mode selections correctly, which is primarily a convenience concern.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0956 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission / Mode Selection
Difficulty
Type
Generic (SAE)
Recommended Tools
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