Honda P1607 Code: ECM/PCM Internal Circuit Malfunction A
The Honda engine computer's self-test found a fault inside its own circuitry.
At a glance
Severity: Moderate
- Meaning
- ECM/PCM Internal Circuit Malfunction A
- System
- ECU & Outputs · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $20–$1,500
- DIY difficulty
- Hard
Honda's PCM constantly checks its own processor, memory and internal driver circuits. P1607 means one of those self-checks failed, so the computer itself is reporting a hardware or internal circuit problem. Before condemning an expensive part, it's important to rule out outside causes that can make a healthy PCM fail its self-test: a weak battery, poor main grounds, voltage spikes from jump-starting, water that reached the connectors, or an aftermarket or mismatched ECU. When P1607 returns instantly with the key on and the engine off, even after those checks, the PCM is almost always at fault; cracked solder joints that open up in cold weather are a known pattern on older Civics, Accords and Odysseys.
Can I keep driving? Many cars run normally with P1607, but a failing PCM can cause sudden stalling, erratic shifting on automatics or a no-start. Avoid long trips until it's diagnosed, and fix it promptly if you notice any drivability change.
How to read P1607
- P Powertrain
- 1 Manufacturer-specific
- 6 Computer & outputs
- 07 Specific fault
Symptoms
- Check engine light on, sometimes as soon as the key is turned on
- Code returns immediately after clearing
- Occasional stalling, rough running or a hard start, especially when cold
- On automatics, harsh or odd shifting in some cases
- Other unrelated codes appearing and disappearing
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Internal PCM failure such as cracked solder joints or a failed component
- Low or unstable supply voltage from a weak battery or charging fault
- Poor engine or body ground connections
- Water intrusion into the PCM or its connectors from a leak
- Aftermarket, used or mismatched ECU fitted
- PCM software issue on models with a known reprogramming update
Diagnosis step by step
Test battery and charging
The battery should rest at about 12.6 V and hold above roughly 9.6 V while cranking; with the engine running, charging voltage should sit around 13.5 to 14.8 V. Replace a weak battery before going further, then clear the code.
Tools: Multimeter
Check main grounds
Measure voltage drop between the battery negative post and the engine block, and between the post and the body, while cranking. More than about 0.2 to 0.3 V means a ground strap needs cleaning or replacing.
Tools: Multimeter, Screwdriver
Key-on test after clearing
Clear the code and turn the key to on without starting. If P1607 reappears right away, the PCM's self-test fails on its own and outside causes become unlikely; if it only comes back after driving, look harder at voltage, grounds and connectors.
Tools: OBD-II scanner
Inspect the PCM and its connectors
Depending on the model, the PCM sits behind the passenger kick panel, in the footwell or in the engine bay. Look for water stains, corrosion or bent pins, and check the carpet for dampness from a windshield, cowl or door seal leak.
Tools: Flashlight, Screwdriver
Check for updates, then replace and program
A dealer or shop with Honda software can check whether an update exists for your PCM. If not, a replacement PCM must be programmed to the car and registered to the immobilizer, or the engine won't start.
Tools: OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace weak battery | Yes | $150–$300 |
| Clean or replace ground straps | Yes | $20–$150 |
| PCM software update | No | $100–$250 |
| Repair or rebuild of original PCM (mail-in service) | No | $250–$550 |
| New or remanufactured PCM with programming and immobilizer setup | No | $600–$1,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
With the check engine light on, a car with P1607 fails an OBD emissions inspection, and a replaced PCM starts with all monitors not ready. Plan several days of mixed driving after the repair before going for the test.
Frequently asked questions
Does P1607 always mean a new computer?
No. Low voltage, bad grounds and water in the connectors can all make the PCM fail its self-test. If those are ruled out and the code returns the moment the key is turned on, then the PCM is the likely cause.
Can I swap in a used PCM from a junkyard?
Only if it's the correct part for your engine and transmission, and it still needs to be registered to your car's immobilizer. Without that, the engine cranks but won't start.
Why does P1607 show up mostly in cold weather?
Aging solder joints on the circuit board contract in the cold and can lose contact, then reconnect as the cabin warms. That's why some cars set P1607 on cold mornings and seem fine later in the day.
Is P1607 the same as P0606?
They describe similar problems, an internal fault in the engine computer. P0606 is the generic code, while P1607 is Honda's own number used on many of its models.
Sources
- Manufacturer public service information (cross-checked)
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