What Does P256F Mean?
The PCM detects an abnormal signal from the secondary A/C request circuit (circuit B). This may indicate communication issues between the A/C control module and PCM regarding compressor engagement requests.
Common Causes
30%
Failed A/C pressure switch or sensor providing incorrect signal
25%
Wiring issues in A/C request circuit B
20%
Faulty A/C control module sending erratic requests
15%
Refrigerant pressure out of range affecting pressure switches
10%
PCM software calibration issue or PCM failure
Diagnostic Steps
1
Step 1: Monitor A/C request signal status in live data while operating A/C controls
2
Step 2: Check refrigerant pressures with manifold gauges to verify system is within specifications
3
Step 3: Test A/C pressure switch(es) operation and resistance values
4
Step 4: Inspect wiring and connectors between A/C control module, pressure switches, and PCM
5
Step 5: Compare A/C request circuit A and circuit B signals to identify discrepancies
Estimated Repair Cost
$120 - $550
Parts + labor, varies by vehicle and location
The PCM detects an abnormal signal from the secondary A/C request circuit (circuit B). This may indicate communication issues between the A/C control module and PCM regarding compressor engagement requests.
The most common cause of P256F (A/C Request "B" Circuit Range/Performance) is: Failed A/C pressure switch or sensor providing incorrect signal
Typical repair costs for P256F range from $120 to $550, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. A/C system may not function properly or compressor may cycle erratically affecting cabin comfort and fuel economy.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P256F to identify the root cause.
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Quick Info
Category
Powertrain
System
A/C System and Engine Load Management
Difficulty
Type
Generic (SAE)
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