Rick's Free Auto Repair Advice

P1400 Chevrolet

How to fix a P1400 Cold Start Emission Reduction Control System on Chevrolet

If you have a P1400 Chevrolet trouble code, read this article on what the code means and how to fix the problem.

Catalytic converters must be warm before they can work properly. On a cold start the PCM provides a rich mixture to keep the cold engine running. All that extra fuel goes into the catalytic converter. But the exhaust isn’t very hot, because, ah, the engine is pretty cold. GM has employed several strategies to fire up the catalytic converter quicker and reduce cold start emissions. One way is to use a secondary air pump that pumps outside air directly into the catalytic converter. That method dumps extra oxygen into the converter to react with the extra fuel and burn it off. In the process the converter heats up to normal temps. The second method is to adjust idle speed and spark timing.

It’s this second method that can give you a P1400 Chevrolet trouble code. Specifically, when the PCM senses a cold start (any time an engine has been sitting for 3 or more hours) the PCM increases idle speed and retards spark timing. Then the PCM monitors all these values to calculate an exhaust energy model:

Engine speed
Spark advance
Throttle position
Engine airflow
Engine coolant temperature
Engine runtime
Park/neutral position
Vehicle speed

In order to set the P1400 Chevrolet code, all these conditions must be met:

A cold start has been detected.
The vehicle speed is less than 2 km/h.
The engine is at idle with no input from the accelerator pedal.
The airflow per cylinder is greater than 80 mg/cylinder.
DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0220, P0222, P0223, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0335, P0336, P0351, P0352, P0353, P0354, P0355, P0356, P0502, P0506, P0507, P0601, P0602, P0603, P0604, P0606, P0607, P062F, P0641, P0651, P1101, P1516, P1682, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, P2176, P2610 are not set.

This DTC runs for 15 seconds within the first 70 seconds of start up. This diagnostic runs once per trip when a cold start has been determined.

If the actual exhaust energy model does not match the expected exhaust energy model the PCM will set a P1400 Chevrolet trouble code.

In late model vehicles with an electronic throttle body, you should remove the throttle body and perform a complete cleaning of the throttle body bore and throttle plate. Do NOT simply spray throttle body cleaner into the throttle body. That is NOT the recommended procedure. Throttle body solvent can penetrate along the throttle plate shaft and enter the motor/gear area and damage the throttle body. Instead, spray the cleaner on a soft cloth and wipe the parts. When you’re done, perform a throttle body idle relearn procedure to reestablish base idle.

Next, inspect the air filter and air duct along with these items:

Modified, damaged, or restricted air cleaner box and duct
Crankcase ventilation system for correct operation
Vacuum leak and other un-metered air downstream of the mass air flow (MAF) sensor
Intake manifold leak
Damaged, restricted, modified or enhanced exhaust system
Inspect the engine mechanical for items that could alter the air flow into the combustion chamber.

Shops report that a throttle body cleaning, MAF sensor cleaning, and a new air filter usually solves the problem.

©, 2015 Rick Muscoplat

Posted on by Rick Muscoplat

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